Physical Week 5/6 Flashcards
Thermodynamics and Rates
1
Q
What is the enthalpy of atomisation?
A
The enthalpy of atomisation of an element is the enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state.
2
Q
What does it mean to have an ionic nature with covalent characteristics?
A
When a compound has covalent characteristics, it leans towards a giant covalent structure, making the lattice stronger compared to a 100% ionic compound.
3
Q
What are Born-Haber cycles?
A
Born Haber cycles are a series of steps used to calculate the lattice enthalpy of an ionic compound indirectly by using available data changes and connecting them in a cycle.
4
Q
What is the enthalpy change of formation?
A
The enthalpy change of formation is the energy change when 1 mole of a compound is formed from its elements in their standard states.
5
Q
What is the first electron affinity?
A
The first electron affinity is the enthalpy change that occurs when 1 mole of gaseous atoms gain 1 mole of electrons to form 1 mole of gaseous ions with a -1 charge.
6
Q
What is the enthalpy of lattice formation?
A
The enthalpy of lattice formation is the standard enthalpy change when 1 mole of an ionic crystal lattice is formed from its constituent ions in gaseous form.
7
Q
What is meant by the solubility of ionic substances?
A
The solubility of ionic substances refers to their ability to dissolve in a solvent, usually water, to form a homogeneous solution.
8
Q
What is the standard enthalpy change of formation?
A
The standard enthalpy change of formation of a compound is the energy transferred when 1 mole of the compound is formed from its elements under standard conditions (298K and 100kPa), all reactants and products being in their standard states.
9
Q
What is meant by a covalent influence on the lattice and Bornn-Haber value?
A
When a compound exhibits some covalent characteristics, it affects the lattice enthalpy and the Born-Haber value. The greater the covalent character, the larger the difference between the theoretical and Born-Haber values.
10
Q
What is polarising power?
A
The polarising power of a cation refers to its ability to polarise a negative ion. It increases when the positive ion is small or carries multiple charges.
11
Q
What is the purpose of the Born Haber cycle in chemistry?
A
The Born Haber cycle is a method used in chemistry to indirectly calculate the enthalpy of lattice formation of an ionic compound.
12
Q
Why is the formula of calcium chloride CaCl2 and not CaCl or CaCl3?
A
The formula of calcium chloride is CaCl2 because it has the most exothermic enthalpy of formation compared to CaCl and CaCl3.
13
Q
What does the Born-Haber cycle for CaCl reflect about the enthalpy of formation?
A
The Born-Haber cycle for CaCl reflects that the enthalpy of formation is mainly influenced by the ionisation energy and lattice enthalpy.
14
Q
What are the different enthalpy changes involved in the Born Haber cycle?
A
The Born Haber cycle involves a series of enthalpy changes, including formation, atomisation, ionisation, and electron affinity.
15
Q
Why is CaCl2 the most thermodynamically stable option?
A
CaCl2 is the most thermodynamically stable option due to the stronger lattice formation energy outweighing the higher ionisation energy needed for Ca2+ formation.
16
Q
How does the polarising power of a cation affect the negative ion in an ionic compound?
A
The polarising power of a cation increases when it is small or carries multiple charges, causing distortion and polarisation of the negative ion in an ionic compound.
17
Q
How can the enthalpy of lattice formation be determined using the Born Haber cycle?
A
By applying Hess’s law and using available data, the enthalpy of lattice formation can be determined.
18
Q
What is the relationship between the theoretical lattice enthalpies and the positive charge on the calcium ion?
A
The theoretical lattice enthalpies for CaCl, CaCl2, and CaCl3 increase as the positive charge on the calcium ion increases.
19
Q
What is the standard enthalpy change of formation of a compound?
A
The energy transferred when 1 mole of the compound is formed from its elements under standard conditions (298K and 100kPa), all reactants and products being in their standard states.
20
Q
When is the Born Haber cycle useful in determining lattice enthalpy?
A
The Born Haber cycle is useful when direct determination of lattice enthalpy is not possible.
21
Q
What is the total entropy change?
A
Total entropy change refers to the overall change in entropy of a system during a chemical process. It takes into account the changes in entropy of all components involved in the process, including the solute, solvent, and surroundings.
22
Q
What is solubility?
A
Solubility refers to the ability of a substance to dissolve in a solvent, usually water. It is influenced by factors such as temperature, pressure, and the nature of the solute and solvent.
23
Q
What is the enthalpy of hydration?
A
The enthalpy of hydration is the enthalpy change when one mole of gaseous ions become hydrated, forming aqueous ions. It represents the energy change associated with the formation of bonds between the ions and water molecules.
24
Q
What is the lattice enthalpy?
A
Lattice enthalpy is the energy change associated with the formation of one mole of an ionic compound from its constituent ions in the gas phase. It represents the energy released when the ions come together to form a solid lattice structure.
25
What is entropy?
Entropy is a measure of the disorder or randomness of a system. In the context of solution chemistry, the dissolution of a solid into ions increases the entropy due to increased disorder and particle count.
26
What is Hess's law?
Hess's Law states that the enthalpy change of a reaction is independent of the pathway taken, as long as the initial and final conditions are the same. It allows us to determine the enthalpy change of a reaction by combining known enthalpy changes of other reactions.
27
What is hydration enthalpy?
Hydration enthalpy is the energy change associated with the formation of one mole of hydrated ions from gaseous ions. It represents the energy released when the ions bond with water molecules to form aqueous ions.
28
What is the enthalpy of solution?
The enthalpy of solution is the standard enthalpy change when one mole of an ionic solid dissolves in a large enough amount of water to ensure that the dissolved ions are well separated and do not interact with one another. It represents the energy change associated with the dissolution process.
29
What is the lattice dissociation enthalpy?
Lattice dissociation enthalpy is the energy required to break the bonds within an ionic structure and convert it into gaseous ions. It is an endothermic process as it requires energy to overcome the attractive forces between the ions in the solid lattice.
30
Is the process of bonding between ions and water molecules exothermic or endothermic?
The process is exothermic as bonds are formed between ions and water molecules.
31
What happens when an ionic structure dissolves in water?
Its bonds within the structure break and new bonds form between the metal ions and water molecules.
32
How does the size and charge of ions affect the magnitude of lattice enthalpy?
The size and charge of ions affect the magnitude of lattice enthalpy.
33
How would you calculate the enthalpy of solution of a compound given the lattice enthalpy of formation and the enthalpies of hydration of its ions?
The enthalpy of solution can be calculated using the formula ΔsolH = - ΔLEH + Σ ΔhydH, where ΔLEH is the lattice enthalpy of formation and Σ ΔhydH is the sum of the enthalpies of hydration of the ions.
34
How can the enthalpy of solution be calculated?
The enthalpy of solution can be calculated using Born Haber cycles and enthalpies of hydration.
35
How does the solubility of a substance relate to the nature of its hydration enthalpy?
The solubility of a substance is influenced by the exothermic or endothermic nature of the hydration enthalpy, with salts having exothermic hydration enthalpies being more likely to dissolve.
36
What is the use of Hess's Law in determining enthalpy changes of solution?
Hess's Law can be used to determine enthalpy changes of solution.
37
What happens to the entropy when a solid dissolves into ions?
Dissolving a solid into ions increases entropy due to increased disorder and particle count.
38
What is lattice dissociation enthalpy?
Lattice dissociation enthalpy is the energy required to break the structure of an ionic substance.
39
What is the definition of enthalpy of hydration?
Enthalpy of hydration is the enthalpy change when gaseous ions become hydrated.
40
What determines the strength of hydration enthalpy?
The strength of hydration enthalpy is determined by the charge density, with smaller ions or those with larger charges having more negative hydration enthalpies.
41
What is the enthalpy of solution?
The standard enthalpy change when one mole of an ionic solid dissolves in a large enough amount of water to ensure that the dissolved ions are well separated and do not interact with one another.
42
What does the comparison of continuous rate graphs show?
Higher concentrations, temperatures, or surface areas result in faster rates, indicated by steeper gradients on graphs. For reactions with excess acid, the final gas volume produced is proportional to the moles of acid.
43
What is the rate constant?
The rate constant, represented by 'k' in the rate equation, is a proportionality constant that relates the rate of a reaction to the concentrations of its reactants. It is specific to a particular temperature and remains constant at that temperature.
44
What is the initial rate?
The initial rate is the fastest rate at the beginning of a reaction. It can be calculated from the slope of a continuous concentration vs. time graph at time = zero.
45
What are continuous rate methods?
Continuous rate methods involve tracking a single experiment over time to record changes in concentration and determine the reaction rate. The gradient of the concentration vs. time graph represents the rate of the reaction.
46
What are reaction orders?
Reaction orders, represented by 'm' and 'n' in the rate equation, determine how the rate of a reaction depends on the concentrations of its reactants. They are usually whole numbers (0, 1, 2) and are determined experimentally
47
What are rate equations?
Rate equations are mathematical expressions that link the rate of a chemical reaction to the concentrations of its reactants. They are determined experimentally and may differ from the stoichiometric coefficients in the balanced equation.
48
What is an excess reactant?
In reactions with multiple reactants, if the concentration of one reactant is significantly higher than the others, it may not affect the reaction rate and can be considered as a pseudo-zero order. This is because its concentration remains almost constant and does not have an impact on the rate.
49
What is the purpose of rate equations in chemistry?
Rate equations in chemistry involve measuring the volume of hydrogen gas produced over time when hydrochloric acid reacts with magnesium.
50
What is the rate constant and how does it vary?
The rate constant (k) is a specific value for a particular temperature and increases with temperature.
51
What do rate equations in chemistry link?
Rate equations in chemistry link the rate of a chemical reaction to the concentrations of its reactants, and are determined experimentally.
52
How are excess reactants with significantly higher concentrations treated in rate equations?
Excess reactants with significantly higher concentrations can be considered as pseudo-zero order as they do not affect the reaction rate.
53
What is the order of a reaction?
The order of reaction refers to the power to which the concentration of a reactant is raised in the rate equation. It can be determined graphically by plotting the logarithm of the rate against the logarithm of the concentration of a reactant.
54
What is a reaction mechanism?
A reaction mechanism is a series of steps that a chemical reaction goes through, including the formation of intermediate compounds. The slowest step in the mechanism, known as the rate-determining step, controls the overall rate of the reaction.
55
What is the rate-determining step?
The rate-determining step is the slowest step in a reaction mechanism and determines the overall rate of the reaction. It is the step with the highest activation energy and controls the rate of the reaction.
56
What is the arrhenius equation?
The Arrhenius equation describes the relationship between the rate constant of a reaction and the temperature. It is given by the equation k = Ae^(-EA/RT), where k is the rate constant, A is the Arrhenius constant, EA is the activation energy, R is the gas constant, and T is the temperature.
57
What is a rate equation?
The rate equation is an equation that relates the rate of a chemical reaction to the concentrations of the reactants. It is determined by conducting a series of experiments where the initial concentrations of reactants are changed one at a time, and the initial rate is measured each time.
58
What is the activation energy?
Activation energy is the minimum amount of energy required for a chemical reaction to occur. It is represented by the symbol Ea and is influenced by temperature.
59
How do changes in concentration affect the rate?
Concentration changes refer to the effect of altering the concentration of a reactant on the rate of a reaction. By observing how the rate changes when the concentration of a reactant is doubled, tripled, or quadrupled, the order of the reaction with respect to that reactant can be determined.
60
What is molecularity?
Molecularity refers to the number of molecules or ions involved in a particular step of a reaction mechanism. It is equal to the sum of the stoichiometric coefficients of the reactants in that step.
61
What is the rate-determining step in a reaction and how does it control the overall rate?
The rate-determining step in a reaction is the slowest step that controls the overall rate. The molecularity of the slowest step determines the order of reaction for each substance involved.
62
What information is needed to calculate the Arrhenius constant, A, in the Arrhenius equation?
To calculate the Arrhenius constant, A, in the Arrhenius equation, the activation energy, Ea, temperature, and gas constant, R, must be known.
63
How can the rate equation for a reaction be determined?
The rate equation for a reaction can be determined by conducting experiments with varying initial concentrations of reactants, and the order of each reactant can be calculated graphically or by observing how changes in concentration affect the rate.
64
What does the Arrhenius equation describe?
The Arrhenius equation describes the relationship between temperature and the rate constant, k.
65
How can the rate constant (k) be calculated using the initial rate data?
The rate constant (k) can be calculated using the initial rate data.
66
What does the rate constant, k, simplify to when the concentration of reactant A is not involved in the rate equation?
The rate constant, k, can be simplified to a constant value when the concentration of reactant A is not involved in the rate equation.
67
What is an intermediate?
In chemistry, an intermediate refers to a compound that is formed in one step of a reaction mechanism and consumed in a subsequent step. It is not one of the reactants or products of the overall reaction but plays a crucial role in the reaction pathway.
68
What is SN1?
SN1 is a term used in organic chemistry to describe a nucleophilic substitution reaction mechanism. It stands for Substitution, Nucleophilic, 1 molecule in the rate-determining step.
69
What is SN2?
SN2 is a term used in organic chemistry to describe a nucleophilic substitution reaction mechanism. It stands for Substitution, Nucleophilic, 2 molecules in the rate-determining step.
70
How is the rate equation in chemistry determined?
The rate equation in chemistry is determined through experimentation by examining the reactant orders and understanding the reaction's mechanism.
71
How does the order of reaction relate to the number of moles of a substance involved in the slowest step?
The order of reaction for each substance corresponds to the number of moles of that substance involved in the slowest step.
72
What is the rate-determining step in a chemical reaction?
The rate-determining step in a chemical reaction is the slowest step among the individual reactions, which governs the overall rate of the entire reaction.
73
What is the equilibrium position?
The equilibrium position refers to the relative concentrations or partial pressures of the reactants and products at equilibrium in a chemical reaction. It is determined by the equilibrium constant and the conditions (such as temperature and pressure) under which the reaction is carried out.
74
What is partial pressure?
Partial pressure refers to the pressure exerted by an individual gas in a mixture of gases. It is similar to the pressure that the gas would have if it occupied the entire space by itself within that mixture.
75
What is concentration?
Concentration refers to the amount of a substance present in a given volume or mass of a solution or mixture. It is typically expressed in units such as moles per liter (mol/L) or grams per liter (g/L).
76
What is a mole fraction?
Mole fraction is a way to express the composition of a mixture. It is calculated by taking the ratio of the number of moles of a particular component to the total number of moles of all components in the mixture.
77
What is the equilibrium constant?
The equilibrium constant is a value that quantifies the extent to which a chemical reaction reaches equilibrium. It is denoted by K and is calculated by taking the ratio of the concentrations or partial pressures of the products to the concentrations or partial pressures of the reactants, each raised to the power of their respective stoichiometric coefficients.
78
What is a homogenous system?
A homogeneous system refers to a system in which the components are uniformly distributed and have the same phase. In the context of equilibrium constants, it refers to a system in which all the reactants and products are in the same phase, typically gases.
79
What is included in the equilibrium constant KP expression?
The equilibrium constant KP is written using the partial pressures of gases only, excluding solids, liquids, and aqueous substances.
80
What is the unit of KP and how is it determined?
The unit of KP is kPa raised to the power of the stoichiometric coefficients of the gases involved in the reaction.
81
How does increasing temperature affect the equilibrium position?
Increasing temperature shifts the equilibrium position towards the endothermic direction.
82
How can the partial pressures of gases in a mixture be calculated?
To calculate the partial pressures of gases in a mixture, use the mole fraction of each gas multiplied by the total pressure.
83
Do changes in pressure or concentration affect the values of Kp or Kc?
No, changes in pressure or concentration do not affect the values of Kp or Kc. Only temperature has an impact on these constants.
84
What is the partial pressure of a gas in a mixture?
The partial pressure of a gas in a mixture is similar to the pressure that the gas would have if it occupied the entire space by itself within that mixture.
85
What is the relationship between the partial pressure of a gas in a mixture and the pressure it would have if it occupied the entire space within the mixture?
The partial pressure of a gas in a mixture is equivalent to the pressure it would have if it occupied the entire space within the mixture.
86
How is the total pressure of a gas mixture related to the partial pressures of the individual gases?
The total pressure of a gas mixture is the sum of the partial pressures of the individual gases.
87
Does increasing pressure change the value of Kp?
No, increasing pressure affects the equilibrium position but does not change the value of Kp.
88
What are secondary rechargeable cells?
Secondary rechargeable cells are electrochemical cells that can be recharged by reversing the reaction. These cells are commonly used in devices like smartphones and laptops.
89
What is a standard hydrogen electrode?
The Standard Hydrogen Electrode (SHE) is a reference electrode used to measure the electrode potential of other electrodes. It consists of a platinum electrode coated with platinum black, immersed in a solution of hydrogen ions (H+) at a concentration of 1.0 mol dm^-3.
90
What is a salt bridge?
A salt bridge is a component of an electrochemical cell that connects the two half-cells. It allows ions to move between the half-cells, maintaining electrical neutrality and preventing unwanted reactions between the electrodes and solutions.
91
What is the voltage?
Voltage, also known as potential difference, is the electric potential energy per unit charge. In an electrochemical cell, voltage is generated by the difference in the tendency of the two half-cells to undergo oxidation or reduction.
92
What is a cell diagram?
A cell diagram is a symbolic representation of an electrochemical cell. It includes the symbols for the electrodes, the phases of the substances involved (solid, liquid, gas), and the presence of a salt bridge.
93
What are electrochemical cells?
Electrochemical cells are devices that convert chemical energy into electrical energy through redox reactions. They consist of two half-cells, each containing a metal electrode and a solution of that metal.
94
What are fuel cells?
Fuel cells are electrochemical devices that convert the chemical energy of a fuel, such as hydrogen, into electrical energy. They operate by combining a fuel (e.g., hydrogen) with oxygen to produce water and generate electricity.
95
What is an electrode potential?
Electrode potential is the measure of the tendency of an electrode to undergo oxidation or reduction. It is the potential difference between an electrode and a reference electrode, such as the Standard Hydrogen Electrode (SHE).
96
What are primary non-rechargeable cells?
Primary non-rechargeable cells are electrochemical cells that cannot be recharged. Their reactions are non-reversible.
97
What is cell EMF?
Cell EMF (Electromotive Force) is the voltage or potential difference between the two electrodes of an electrochemical cell. It is calculated by subtracting the oxidation potential of the anode from the reduction potential of the cathode.
98
What is the significance of standard electrode potentials in understanding redox reactions?
Standard electrode potentials are important in understanding the tendency of species to gain or lose electrons in reactions. They can be used to calculate the electromotive force (EMF) of a cell and indicate the direction of spontaneous changes in redox reactions.
99
What is the effect of reactant concentrations on Ecell for most cells that are exothermic in the spontaneous direction?
For most cells that are exothermic in the spontaneous direction, increasing reactant concentrations raises Ecell, while decreasing them lowers Ecell.
100
Why is platinum chosen as an electrode?
Platinum is chosen as an electrode because it is unreactive and conducts electricity effectively.
101
What does Ecell measure and how is it related to the likelihood of a cell reaction occurring?
Ecell measures how far the cell reaction is from equilibrium. A more positive Ecell indicates a greater likelihood of the reaction occurring.
102
What is the difference between primary non-rechargeable cells and secondary rechargeable cells?
Primary non-rechargeable cells have non-reversible reactions, while secondary rechargeable cells can be recharged by reversing the reaction.
103
What are some common secondary standards with specific electrode potentials?
What are some common secondary standards with specific electrode potentials?
104
What is the purpose of a salt bridge in an electrochemical cell?
The salt bridge connects the two half-cells in the cell, allowing ions to move and preventing unwanted reactions between the electrodes and solutions.
105
How would you measure the potential difference between two electrodes?
By connecting an electrode to another half-cell with a known potential and measuring the potential difference between them.
106
How would you convert a non-rechargeable cell into a rechargeable one?
It's not possible to convert a non-rechargeable cell into a rechargeable one
107
Why is a platinum electrode included in electrochemical cells that lack metal electrodes?
In systems without metal electrodes, a platinum electrode must be included in the cell diagram to facilitate the flow of electrons and complete the circuit.
108
What are the advantages of hydrogen fuel cells?
Hydrogen fuel cells have several advantages. They produce less pollution and CO2 emissions compared to traditional combustion-based energy sources.
109
What are some sources of hydrogen for hydrogen fuel cells?
Hydrogen can be sourced for fuel cells through water electrolysis, although this method can be costly. To be considered 'green,' the electricity required for water electrolysis must come from renewable sources.
110
What is an ethanol fuel cell?
Ethanol fuel cells are a type of fuel cell that uses ethanol as the fuel. Ethanol is produced from a renewable source, and there is an abundance of raw materials available for ethanol production through fermentation.
111
How do lithium-ion cells eliminate the need for a solvent like water?
Lithium-ion cells use powdered graphite as a support for the reactions, eliminating the need for a solvent like water.
112
What is a characteristic of non-rechargeable cells?
Non-rechargeable cells cannot reverse the reactions inside them.
113
What is required for hydrogen fuel cells to maintain a constant voltage?
Hydrogen fuel cells require a continuous supply of hydrogen and oxygen to maintain a constant voltage.
114
How can electrochemical cells be classified?
Electrochemical cells can be classified as non-rechargeable and rechargeable cells.
115
What happens in a hydrogen fuel cell when higher temperatures are applied?
Using higher temperatures can speed up the reaction, but since it releases heat (exothermic), applying Le Chatelier's principle would result in a decrease in E cell.
116
What is the main difference between non-rechargeable and rechargeable electrochemical cells?
Non-rechargeable cells have reactions inside them that cannot be reversed, while rechargeable cells can be reused multiple times as their reactions can be reversed.
117
How do fuel cells generate voltage?
Fuel cells generate voltage through fuel and oxygen reactions.
118
What are some advantages of using ethanol as a fuel in electrochemical cells?
Ethanol is produced from a renewable source, there is an abundance of raw materials available for its production, it is safer to store compared to hydrogen, and it can utilize the existing infrastructure of petrol stations.
119
What effect does increasing the temperature have on hydrogen fuel cells?
Increasing the temperature of hydrogen fuel cells can speed up the reaction, but it may decrease the cell voltage.
120
What is the role of powdered graphite in lithium-ion cells?
The reagents in the cell stick to powdered graphite, which serves as a support. This base enables the ions to react without needing a solvent like water.
121
What are some of the challenges associated with electrochemical cells?
Expensive, hydrogen storage and transport issues, short lifespan, high production costs, use of toxic chemicals in production
122
Give an example of a non-rechargeable cell.
An example of a non-rechargeable cell is a primary cell.
123
What are some advantages of hydrogen fuel cells?
Hydrogen fuel cells have advantages such as lower pollution and higher efficiency, but they also face challenges like expensive production and storage issues.
