Revision Flashcards
1
Q
What does Hess’s Law allow us to calculate?
A
Hess’s Law allows us to calculate the standard enthalpy change of a reaction from known standard enthalpy changes.
2
Q
Define Hess’s Law.
A
Hess’s Law states that the total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place as long as the initial and final conditions are the same.
3
Q
In terms of bond making and breaking, why is a reaction endothermic?
A
A reaction is endothermic because more energy is required to break bonds than the energy released when new bonds are formed.
4
Q
True or False?
A reaction is exothermic if more energy is released when new bonds are formed than the energy required to break bonds.
A
True.
A reaction is exothermic if more energy is released when new bonds are formed than the energy required to break bonds.
5
Q
State the equation for calculating enthalpy change of reaction using bond energies.
A
The equation for calculating enthalpy change of reaction using bond energies is:
ΔH = Σ(bonds broken) - Σ(bonds formed)
6
Q
Define average bond energy.
A
Average bond energy is the energy needed to break one mole of bonds in a gaseous molecule averaged over similar compounds.
7
Q
True or False?
Bond breaking is an exothermic process.
A
False.
Bond breaking is an endothermic process.
8
Q
Define the term bond dissociation enthalpy.
A
Bond dissociation enthalpy is the energy required to break a particular chemical bond.
9
Q
True or False?
When using cycles to solve Hess’s Law problems, if you follow the direction of the arrow you subtract the quantity.
A
False.
When using cycles to solve Hess’s Law problems, if you follow the direction of the arrow you add the quantity.
10
Q
True or False?
In Hess’s Law calculations, you always need to adjust for different molar amounts.
A
True.
In Hess’s Law calculations, you always need to adjust for different molar amounts.
11
Q
State the general equation for solving Hess’s Law problems using equations.
A
The general equation for solving Hess’s Law problems using equations is:
ΔH(reaction) = Σ(ΔH products) - Σ(ΔH reactants)
12
Q
Define standard enthalpy of formation.
A
The standard enthalpy of formation is the enthalpy change when one mole of a compound is formed from its elements under standard conditions.
13
Q
True or False?
In enthalpy of formation cycles, arrows always point downwards.
A
False.
In enthalpy of formation cycles, arrows always point upwards because the definition of enthalpy of formation must go from elements to compounds.
14
Q
State the equation used to calculate enthalpy changes from enthalpy of formation data.
A
The equation used to calculate enthalpy changes from enthalpy of formation data is:
ΔH = ΣΔHfꝊ(products) - ΣΔHfꝊ(reactants)
15
Q
The enthalpy of formation of elements in their standard states is always ______.
A
The enthalpy of formation of elements in their standard states is always zero.
16
Q
Define standard enthalpy of combustion.
A
Standard enthalpy of combustion is the enthalpy change that occurs when one mole of a substance burns completely under standard conditions.
17
Q
True or False?
In enthalpy of combustion cycles, arrows always point upwards.
A
False.
In enthalpy of combustion cycles, arrows should be pointing downwards. (Houses burn DOWN)
18
Q
What is the general equation for calculating ΔH using enthalpy of combustion data?
A
The general equation for calculating ΔH using enthalpy of combustion data is:
ΔH = ΣΔHcꝊ(reactants) - ΣΔHcꝊ(products)
19
Q
The general equation for calculating ΔH using enthalpy of combustion data is:
ΔH = ΣΔHcꝊ(reactants) - ΣΔHcꝊ(products)
A
The enthalpy of combustion is always an exothermic process.
20
Q
The sign for enthalpy change of combustion values will always be _____.
A
The sign for enthalpy change of combustion values will always be negative.
21
Q
True or False?
Enthalpy of combustion can be used to calculate enthalpy of formation.
A
True.
Enthalpy of combustion can be used to calculate enthalpy of formation using Hess’s Law.
22
Q
What is the significance of enthalpy of combustion in practical applications?
A
Enthalpy of combustion is significant in practical applications as it helps determine the energy content of fuels and food.
23
Q
What is a Born-Haber cycle?
A
A Born-Haber cycle is a specific application of Hess’s Law for ionic compounds that enables the calculation of lattice enthalpy.
24
Q
True or False?
The first ionisation energy is always an exothermic process.
A
False.
The first ionisation energy is always an endothermic process.
25
Define the term lattice enthalpy.
Lattice enthalpy is the energy required to separate one mole of an ionic compound into its constituent gaseous ions.
26
What is the enthalpy of atomisation?
The enthalpy of atomisation is the energy required to convert one mole of an element in its standard state to gaseous atoms.
27
The energy change when one mole of gaseous atoms gains one mole of electrons to form one mole of gaseous anions is known as ____.
The energy change when one mole of gaseous atoms gains one mole of electrons to form one mole of gaseous anions is known as electron affinity
28
In a Born-Haber cycle for NaCl, what does an arrow from Na (s) to Na (g) represent?
In a Born-Haber cycle for NaCl, the arrow from Na (s) to Na (g) represents the enthalpy of atomisation of sodium.
29
True or False?
Arrows pointing upwards in a Born-Haber cycles represent endothermic reactions.
True.
Arrows pointing upwards in a Born-Haber cycles represent endothermic reactions.
30
Write an equation to represent the first electron affinity of chlorine.
An equation to represent the first electron affinity of chlorine is:
Cl (g) + e- → Cl- (g)
31
Write an equation to represent the second ionisation energy of magnesium.
An equation to represent the second ionisation energy of magnesium:
Mg+ (g) → Mg2+ (g) + e-
32
What is the enthalpy of atomisation of chlorine?
ΔHθBE Cl2 = 242 kJ mol-1
The enthalpy of atomisation of chlorine is 121 kJ mol-1:
ΔHθat Cl2 = 242 / 2 = 121 kJ mol-1
33
Calculate the enthalpy change for the following conversion:
Ca (s) → Ca2+ (g) + 2e-
ΔHθIE1 Ca = 590 kJ mol-1
ΔHθIE2 Ca = 1145 kJ mol-1
ΔHθat Ca = 178 kJ mol-1
To calculate the enthalpy change for the following conversions:
Ca (s) → Ca2+ (g) + 2e-
ΔHθIE1 Ca = 590 kJ mol-1
ΔHθIE2 Ca = 1145 kJ mol-1
ΔHθat Ca = 178 kJ mol-1
ΔHθat Ca + ΔHθIE1 Ca + ΔHθIE2 Ca = 178 + 590 + 1145 = (+)1913 (kJ mol-1)
34
True or False?
When performing a Born-Haber cycle calculation for MgCl2, the value for the first electron affinity of chlorine would need to be doubled.
True.
When performing a Born-Haber cycle calculation for MgCl2, the value for the first electron affinity of chlorine would need to be doubled.
35
Calculate the enthalpy change for the following conversion:
Cl2 (g) + 2e- → 2Cl- (g)
ΔHθBE Cl2 = 242 kJ mol-1
ΔHθEA Cl = -349 kJ mol-1
To calculate the enthalpy change for the following conversion:
Cl2 (g) + 2e- → 2Cl- (g)
ΔHθBE Cl2 = 242 kJ mol-1
ΔHθEA Cl = -349 kJ mol-1
ΔHθBE Cl2 + (2 x ΔHθEA Cl) = 242 + (2 x -349) = -456 (kJ mol-1)
36
Rearrange the following equation to calculate lattice enthalpy, ΔHꝋlat.
ΔHꝋf = ΔHꝋat + ΔHꝋat + ΔHꝋIE + ΔHꝋEA - ΔHꝋlat
To calculate lattice enthalpy, ΔHꝋlat:
ΔHꝋf = ΔHꝋat + ΔHꝋat + ΔHꝋIE + ΔHꝋEA - ΔHꝋlat
ΔHꝋlat = - ΔHꝋf + ΔHꝋat + ΔHꝋat + ΔHꝋIE + ΔHꝋEA
37
What is the rate equation?
What is the rate equation?
The following reaction will be used to discuss rate equations:
A (aq) + B (aq) → C (aq) + D (g)
The rate equation for this reaction is:
Rate of reaction = k [A]m [B]n
Rate equations depend on the mechanism of the reaction and can only be determined experimentally, they cannot be found from the stoichiometric equations
In the above rate equation:
[A] and [B] are the concentrations of the reactants
m and n are orders with respect to each reactant involved in the reaction
Products and catalysts may feature in rate equations
Intermediates do not feature in rate equations
38
What is the order of reaction?
The order of a reactant shows how the concentration of a chemical, typically a reactant, affects the rate of reaction
It is the power to which the concentration of that reactant is raised in the rate equation
The order can be a positive, negative or fractional value
Orders that are a fraction suggest that the reaction involves multiple steps
39
Zero order
When the order of reaction with respect to a chemical is 0
Changing the concentration of the chemical has no effect on the rate of the reaction
Therefore, it is not included in the rate equation
40
First order
When the order of reaction with respect to a chemical is 1
The concentration of the chemical is directly proportional to the rate of reaction, e.g. doubling the concentration of the chemical doubles the rate of reaction
The chemical is included in the rate equation
41
Second order
When the order of reaction with respect to a chemical is 2
The rate is directly proportional to the square of the concentration of that chemical, e.g. doubling the concentration of the chemical increases the rate of reaction by a factor of four
The chemical is included in the rate equation (appearing as a squared term)
42
Overall order
The overall order of reaction is the sum of the powers of the reactants in a rate equation (m + n)
43
The chemical equation for the thermal decomposition of dinitrogen pentoxide is:
2N2O5 (g) → 4NO2 (g) + O2 (g)
The rate equation for this reaction is:
Rate = k[N2O5 (g)]
1. State the order of the reaction with respect to dinitrogen pentoxide
2. Deduce the effect on the rate of reaction if the concentration of dinitrogen pentoxide is tripled
1. Dinitrogen pentoxide features in the rate equation, therefore, it cannot be order zero / 0
The dinitrogen pentoxide is not raised to a power, which means that it cannot be order 2 / second order
Therefore, the order with respect to dinitrogen pentoxide must be order 1 / first order
2. Since the reaction is first order, the concentration of dinitrogen pentoxide is directly proportional to the rate
This means that if the concentration of the dinitrogen pentoxide is tripled, then the rate of reaction will also triple
44
The following equation represents the oxidation of bromide ions in acidic solution
BrO3- (aq) + 5Br- (aq) + 6H+ (aq) → 3Br2 (l) + 3H2O (l)
The rate equation for this reaction is:
Rate = k[BrO3- (aq)][Br- (aq)][H+ (aq)]
1. State the overall order of the reaction
2. Deduce the effect on the rate of reaction if the concentration of bromate ions is doubled and the concentration of bromide ions is halved
1. All three reactants feature in the rate equation but they are not raised to a power, this means that the order with respect to each reactant is order 1 / first order
The overall order of the reaction is 1 + 1 + 1 = 3 or third order
2. Since each reactant is first order, the concentration of each reactant is directly proportional to the effect that it has on rate
If the concentration of the bromate ion is doubled, then the rate of reaction will also double
If the concentration of the bromide ion is halved then the rate will also halve
Therefore, there is no overall effect on the rate of reaction - one change doubles the rate and the other change halves it
45
Define rate of reaction.
Rate of reaction is the speed at which a chemical reaction takes place, expressed as the change in concentration of a particular reactant or product per unit time.
46
What are the typical units for rate of reaction?
Typical units for rate of reaction are mol dm^-3 s^-1.
47
What is the equation for calculating rate of reaction?
The equation for calculating rate of reaction is:
Rate of reaction = change in concentration of reactants or products / time
48
How can you find the rate of reaction at a particular time on a graph?
You can find the rate of reaction at a particular time by calculating the gradient of the tangent to the curve at that time.
49
What does the equation gradient = Δy / Δx represent in rate of reaction graphs?
The equation gradient = Δy / Δx represents the calculation of the gradient of the tangent to the curve, which gives the rate of reaction at a specific time.
50
What are three commonly used techniques for measuring rates of reaction?
Three commonly used techniques for measuring rates of reaction are:
Mass loss
Gas production
Colorimetry.
51
According to collision theory, what are the four factors that influence the rate of a chemical reaction?
According to collision theory, the four factors that influence the rate of a chemical reaction according to collision theory are:
Collision frequency,
Collision energy,
Activation energy,
Collision geometry.
52
State three ways that the collision frequency of a given system can be changed.
Three ways that the collision frequency of a given system can be changed include:
Changing the concentration of the reactants
Changing the total pressure
Changing the temperature
Changing the surface area of the reacting particles
53
What are the five factors affecting the rate of reaction?
The five factors affecting the rate of reaction are:
Concentration,
Pressure,
Temperature,
Surface area,
The use of catalysts.
54
Define catalyst in terms of its effect on reaction rate.
A catalyst is a substance that provides the reactants with an alternative reaction pathway which is lower in activation energy than the uncatalyzed reaction, increasing the rate of reaction.
55
Define activation energy.
Activation energy (Ea) is the minimum amount of energy that reactant particles need to overcome for a reaction to take place.
56
If a reversible reaction is exothermic in the forward direction, how can the activation energy of the reverse reaction be calculated?
If a reversible reaction is exothermic in the forward direction, the activation energy of the reverse reaction is:
Ea (reverse) = ∆H + Ea (forward)
57
If a reversible reaction is endothermic in the forward direction, how can the activation of the reverse reaction be calculated?
If a reversible reaction is endothermic in the forward direction, the activation of the reverse reaction is:
Ea (reverse) = Ea (forward) - ∆H
58
How does an energy profile show that a reaction is exothermic?
An energy profile shows that a reaction is exothermic because the energy of the products is lower than the energy of the reactants.
59
How does an energy profile show that a reaction is endothermic?
An energy profile shows that a reaction is endothermic because the the energy of the products is higher than the energy of the reactants.
60
What is a Maxwell-Boltzmann distribution curve?
A Maxwell-Boltzmann distribution curve is a graph that shows the distribution of energies of particles in a sample at a certain temperature.
61
What is the rate equation?
The rate equation is an expression that shows how the rate of a reaction depends on the concentration of reactants and a rate constant.
62
Define the term rate constant.
The rate constant (k) is a proportionality constant that links the rate of reaction to reactant concentrations.
63
Write the rate equation for a reaction that is first order with respect to [A] and zero order with respect to [B].
The rate equation for a reaction that is first order with respect to [A] and zero order with respect to [B] is:
Rate = k [A]
64
The rate equation for a reaction that is first order with respect to [A] and zero order with respect to [B] is:
Rate = k [A]
Concentration change from 0.15 mol dm-3 to 0.30 mol dm-3
Concentration doubles
Rate of reaction change from 1.2 x 10-2 mol dm-3 s-1 to 4.8 x 10-2 mol dm-3 s-1
Rate of reaction increases by a factor of 4
Therefore, A is second order.
65
The rate equation for a chemical reaction is:
Rate = k [A]2 [B]
What is the overall order of the reaction?
The overall order of reaction is 2 + 1 = 3.
66
The rate equation for a chemical reaction is:
Rate = k [A] [B]
If the concentration of both chemicals is halved, what is the effect on the rate of reaction?
Rate = k [A] [B]
If the concentration of both chemicals is halved, the rate of reaction decreases by a factor of 4.
67
What does a horizontal line on a rate-concentration graph indicate?
A horizontal line on a rate-concentration graph indicates a zero-order reaction with respect to that reactant.
68
True or False?
A first-order reaction shows a straight diagonal line on a rate-concentration graph.
True.
A first-order reaction shows a straight diagonal line on a rate-concentration graph.
69
What shape does a second-order reaction show on a rate-concentration graph?
A second-order reaction shows a curved line on a rate-concentration graph.
70
What does the shape of a concentration-time graph indicate about the reaction order?
The shape of a concentration-time graph indicates the order of the reaction:
A straight line for zero-order
A shallow curve for first-order
A steep curve for second-order.
71
What is the rate constant, k?
The rate constant, k, is a proportionality constant in the rate equation that relates the rate of reaction to reactant concentrations.
72
What are the units of the rate constant for a zero-order reaction?
The units of the rate constant for a zero-order reaction are mol dm⁻³ s⁻¹.
73
What are the units of the rate constant for a first-order reaction?
The units of the rate constant for a first-order reaction are s⁻¹.
74
What are the units of the rate constant for a second-order reaction?
The units of the rate constant for a second-order reaction are mol⁻¹ dm³ s⁻¹.
75
What is a reaction mechanism?
A reaction mechanism is the sequence of elementary steps that describe how a chemical reaction occurs at the molecular level.
76
True or False?
The sum of elementary steps must equal the overall reaction equation.
True.
The sum of elementary steps must equal the overall reaction equation.
77
What is the rate-determining step in a reaction mechanism?
The rate-determining step is the slowest step in a reaction mechanism, which controls the overall rate of the reaction.
78
How does the rate-determining step relate to the rate equation?
The rate-determining step determines which reactants appear in the rate equation and their respective orders.
79
What information is needed to predict a possible reaction mechanism?
To predict a possible reaction mechanism, you need:
The overall reaction equation
The experimentally determined rate equation.
80
What is the overall reaction equation, using the following proposed elementary steps?
Step 1: NO2 + NO2 → NO3 + NO
Step 2: NO3 + CO → NO2 + CO2
Step 1: NO2 + NO2 → NO3 + NO
Step 2: NO3 + CO → NO2 + CO2
The overall reaction equation, using the proposed elementary steps, is:
NO2 + CO → NO + CO2
81
True or False?
2NO2 + F2 → 2NO2F Rate = k [NO2] [F2]
A possible mechanism for the above reaction could include the following elementary steps:
NO2 + F2 → NO2F + F
NO2 + F → NO2F
True.
2NO2 + F2 → 2NO2F Rate = k [NO2] [F2]
A possible mechanism for the above reaction could include the following elementary steps:
NO2 + F2 → NO2F + F
NO2 + F → NO2F
The elementary steps combine, losing F on both sides, to give the overall equation.
82
2N2O5 + O2 → 4NO2 + O2 Rate = k [N2O5]
Explain which of the following elementary steps is the rate-determining step.
Step 1: N2O5 → 2NO2 + O
Step 2: N2O5 + O → 2NO2 + O2
2N2O5 + O2 → 4NO2 + O2 Rate = k [N2O5]
Step 1: N2O5 → 2NO2 + O
Step 2: N2O5 + O → 2NO2 + O2
Step 1 is the rate-determining step because it is the elementary step containing the species and stoichiometry that match the rate equation.
83
How is the rate-determining step represented on an energy profile diagram?
The rate-determining step is represented by the highest activation energy barrier on an energy profile diagram for a multi-step reaction.
84
The Arrhenius equation is k = Ae(-Ea/RT)
What do the terms k, A, Ea, R and T represent in the Arrhenius equation?
In the Arrhenius equation, the terms k, A, Ea, R and T represent:
k is the rate constant
A is the Arrhenius factor
Ea is the activation energy
R is the gas constant
T is the temperature in Kelvin.
85
What does the Arrhenius factor, A, represent?
The Arrhenius factor, A, represents the frequency of collisions with proper orientations for a reaction to occur.
86
True or False?
The activation energy, Ea, in the Arrhenius equation is always constant for a given reaction.
True.
The activation energy, Ea, in the Arrhenius equation is always constant for a given reaction.
87
True or False?
The natural logarithm form of the Arrhenius equation, ln(k) = ln(A) - (Ea/RT), is used to simplify calculations and for analysing graphs.
True.
The natural logarithm form of the Arrhenius equation, ln(k) = ln(A) - (Ea/RT), is used to simplify calculations and for analysing graphs.
88
How does the natural logarithm form of the Arrhenius equation, ln(k) = ln(A) - (Ea/RT), compare to the equation of a straight line, y = mx + c?
When comparing ln(k) = ln(A) - (Ea/RT) to y = mx + c:
ln(k) = y
-Ea/R = m
1/T = x
ln(A) = c
89
How can the Arrhenius factor, A, be determined experimentally?
The Arrhenius factor, A, can be determined experimentally by plotting ln(k) against 1/T and finding the y-intercept, which equals ln(A).
90
What type of graph is used to determine activation energy using the Arrhenius equation?
A graph of ln(k) against 1/T is used to determine activation energy using the Arrhenius equation.
91
True or False?
The slope of the Arrhenius plot, ln(k) vs 1/T, is equal to the activation energy.
False.
The slope of the Arrhenius plot, ln(k) vs 1/T, is equal to -Ea/R, where Ea is the activation energy and R is the gas constant.
92
True or False?
The activation energy calculated from an Arrhenius plot is typically expressed in kJ/mol.
True.
The activation energy calculated from an Arrhenius plot is typically expressed in kJ/mol.
93
Define the term dynamic equilibrium.
Dynamic equilibrium is where the rate of the forward reaction equals the rate of the reverse reaction, and the concentrations of reactants and products remain constant.
94
Define the term closed system.
Define the term open system.
A closed system is a system where none of the reactants or products can enter or leave the reaction vessel.
An open system is a system where the reactants or products can both enter or leave the reaction vessel.
Dynamic equilibrium can only occur in a closed system as none of the reactants or products are able to leave the reaction vessel
95
If the forward reaction of a reversible reaction is exothermic, what is the energy change of the reverse reaction?
If the forward reaction of a reversible reaction is exothermic, the reverse reaction is endothermic.
96
Define the equilibrium constant expression.
The equilibrium constant expression is an equation that links the equilibrium constant, K, to the concentrations of reactants and products at equilibrium, taking into account the stoichiometry of the equation.
97
State the general form of the equilibrium constant expression for the reaction
aA + bB ⇌ cC + dD.
The general form of the equilibrium constant expression is:
K = [C]c [D]d / [A]a [B]b
98
True or False?
Solids are included in equilibrium constant expressions.
False.
Solids are ignored in equilibrium constant expressions.
99
What do the square brackets represent in the equilibrium constant expression?
The square brackets represent the equilibrium concentrations of the substances in mol dm-3.
100
What happens to the equilibrium constant expression when a reaction equation is reversed?
When a reaction equation is reversed, the equilibrium constant becomes the reciprocal of the original K value.
101
What units are typically used for concentrations in equilibrium constant expressions?
Concentrations in equilibrium constant expressions are typically expressed in mol dm-3.
102
What does the size of the equilibrium constant, K, indicate?
The size of the equilibrium constant, K, indicates how the equilibrium mixture is made up with respect to reactants and products.
When K > 1, the equilibrium lies to the right hand side (products are favored).
When K >> 1, the equilibrium lies far over to the right hand side and the reaction almost goes to completion.
When K < 1, the concentration of reactants is greater than the concentration of products.
When K = 1, there are significant amounts of both reactants and products, and equilibrium does not lie in favor of either.
103
Is K constant at all temperatures?
No, K is constant at a specified temperature but can change with temperature.
104
Define the relationship between K and K' for reverse reactions.
K' = 1/K or K' = K-1, where K' is the equilibrium constant for the reverse reaction.
105
True or False?
The equilibrium constant, K, is affected by changes in concentration of reactants or products at a given temperature.
False.
The equilibrium constant, K, is not affected by changes in concentration of reactants or products at a given temperature.
106
What is Le Chatelier's principle?
Le Chatelier's principle states that if a change is made to a system at dynamic equilibrium, the position of the equilibrium moves to minimise this change.
107
How does decreasing the concentration of a product affect the equilibrium?
Decreasing the concentration of a product shifts the equilibrium to the right to reduce the effect of the decrease.
108
How does an increase in pressure affect a gas equilibrium?
An increase in pressure shifts the equilibrium in the direction that produces the smaller number of gas molecules.
109
How does an increase in temperature affect an endothermic reaction?
An increase in temperature shifts the equilibrium in the endothermic direction, favoring the products for an endothermic reaction.
110
In the following system, would an increase or decrease in pressure favour the forward reaction?
2A + 2B ⇌ C + D
Increasing the pressure would favour the forward reaction.
This is because there are 4 molecules on the left and side and 2 molecules on the right hand side.
An increase in pressure will favour the side with the fewest number of molecules.
111
If the forward reaction is endothermic, would a high or low temperature increase the yield of products?
If the forward reaction is endothermic, a high temperature would increase the yield of products.
This is because the forward reaction is endothermic. A high temperature would favour the endothermic pathway to oppose the increase.
112
If the concentration of a reactant decreases, how does the equilibrium shift?
Equilibrium shifts to the left to reduce the effect of a decrease in reactant (or an increase in the concentration of product).
113
Define the reaction quotient, Q.
The reaction quotient, Q, is calculated using the same equation as the equilibrium constant expression, but with non-equilibrium concentrations of reactants and products.
114
What does Q = K indicate about a reaction?
When Q = K, the reaction is at equilibrium.
115
If Q < K, in which direction will the reaction proceed?
If Q < K, the reaction will proceed to the right in favor of the products.
116
True or False?
If Q > K, the reaction will favor the formation of products.
False.
If Q > K, the reaction will proceed to the left in favor of the reactants.
117
How can Q be used to determine if a reaction is at equilibrium?
By calculating Q using concentration values and comparing it to K, we can determine if a reaction is at equilibrium (Q = K) or not (Q ≠ K).
118
True or False?
Q can be calculated using initial concentrations of reactants and products.
True.
Q can be calculated using initial concentrations of reactants and products, or concentrations at any point during the reaction.
119
How is concentration calculated from moles and volume?
Concentration (mol dm-3) = amount of substance (mol) / volume (dm3)
120
What is the equilibrium constant for the following reaction?
CH3COOH (I) + C2H5OH (I) ⇌ CH3COOC2H5 (I) + H2O (I)
The equilibrium constant for the reaction is:
K=(H2O)(CH3COOC2H5)/(C2H5OH)(CH3COOH)
121
CH3COOH (I) + C2H5OH (I) ⇌ CH3COOC2H5 (I) + H2O (I)
At equilibrium, the concentrations are:
[CH3COOH] = 0.4 mol dm-3 [C2H5OH] = 0.6 mol dm-3
[CH3COOC2H5] = 0.3 mol dm-3 [H2O] = 0.5 mol dm-3
What is the value of K for this reaction?
The value of K is:
K= [H2O] [CH3COOC2H5] /[C2H5OH] [CH3COOH]
K= 0.5x0.3/0.6x0.4 = 0.625
122
CH3COOH (I) + C2H5OH (I) ⇌ CH3COOC2H5 (I) + H2O (I)
What happens to the concentration of ethanoic acid if the concentration of ethyl ethanoate increases by 0.25 mol dm-3?
CH3COOH (I) + C2H5OH (I) ⇌ CH3COOC2H5 (I) + H2O (I)
If the concentration of ethyl ethanoate increases by 0.25 mol dm-3, the concentration of ethanoic acid decreases by 0.25 mol dm-3.
123
At equilibrium, a 250 cm3 reaction vessel contains 0.15 moles of ethanol.
What is the concentration of ethanol, in mol dm-3?
The concentration of ethanol, in mol dm-3 is:
Concentration = moles / volume in dm3
Concentration = 0.15 / 0.25 = 0.6 mol dm-3
124
True or False?
A negative ΔG° always indicates that K > 1.
True.
A negative ΔG° always indicates that K > 1, meaning the products are favored at equilibrium.
125
What does ΔG° = 0 indicate about the equilibrium constant?
When ΔG° = 0, the equilibrium constant K = 1, meaning neither reactants nor products are favored at equilibrium.
126
True or False?
The relationship between ΔG° and K is temperature-dependent
True.
The relationship between ΔG° and K is temperature-dependent, as shown by the presence of T in the equation ΔG° = -RT ln K.
