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Flashcards in Chapter 9 Deck (94):
1

Define Enthalpy Change, ΔH/ Kjmol-1

A change in heat energy between a system and its surroundings, under standard conditions.

2

What do enthalpy diagrams show?

The enthalpy change during a reaction.

3

Do exothermic reactions have a positive or negative enthalpy value?

NEGATIVE

4

Give two examples of a exothermic reaction.

Combustion or Acid/Base neutralisation reactions.

5

What is an exothermic reaction?

A reaction when energy if given out, so the system looses heat energy.

6

What labels do you need to include on an enthalpy diagram?

.X axis as 'progress of reaction'
.y axis as 'energy'
.Add enthalpy value if given
.Reactants and Products
.Activation energy

7

What is an Endothermic Reaction?

A reaction when energy is put into the system.

8

Name two examples of an endothermic reaction

Decomposition and Photosynthesis

9

Define Activation Energy, Ea

Activation energy is the minimum energy required to start a chemical reaction by breaking bonds.

10

Is Activation Energy, Ea a positive or negative value?

Positive

11

What is the rate of reaction for a small activation energy?

Fast

12

What is the reaction rate for a large activation energy?

Slow

13

What are the four Standard Conditions for enthalpy change?

1. 100 Kpa (1 atm)
2. 298 K (25`)
3. Solutions a 1 moldm-3
4. All reactants and products in their standard states.

14

Define Standard Enthalpy Change of Reaction, ΔrH*

The enthalpy change when molar quantities shown in a chemical equation, react under standard conditions, with all the reactants and products in their standard states.

15

Define Enthalpy Change of Formation, ΔfH*

The enthalpy change when 1 mole of product is formed from its elements under standard conditions, with all he reactants and products in their standard states.

16

What is the usual ΔfH* value for elements ?

Zero

17

Define the standard enthalpy change of Nuetralisation, ΔneutH*

The enthalpy change when an acid and base react to produce 1 mole of H20, under standard conditions, when all products and reactants are in their standard state.

18

Define the standard enthalpy change of combustion,ΔcH*

The enthalpy change when 1 mole of reactant burns completely with oxygen, under standard conditions with all reactants and products in their standard state.

19

What is the approximate value of ΔneutH*?

-57 kjmol-1

20

What is measuring enthalpy changes by experiment called?

Calorirmetry

21

What are the two common experiments for calculating enthalpy change?

Coffee Cup calorimeter
Flame Calorimeter

22

What experiment can calculate enthalpy change that cannot be used in a college environment?

Bomb Calorimeter

23

What is the equation for calculating Enthalpy Change from experimental results?

q=mcΔT

24

What does the 'q' in q=mcΔt mean?

Energy released/ absorbed by reaction

25

What does the 'm' in q=mcΔt mean?

Mass of water in grams

26

What does the 'c' in q=mcΔt mean?

Specific heat capacity of water (4.18 jg-1k-1)

27

What does the 'ΔT' in q=mcΔT mean?

Change in temperature (kelvin or Celsius as they're equal)

28

What is the equation to calculate ΔH?

ΔH = q/n

29

What does ΔH mean ?

Enthalpy Change

30

What is a cooling curve used for?

A cooling curve is used to increase the accuracy of the ΔH value obtained from the experimental results, as it correct experimental errors.

31

How do you calculate ΔT?

ΔT= T final- T initial

32

What are two errors in calculating the enthalpy change of reaction, ΔrH?

Heat loss to the surroundings

Method assumes all solutions have the same specific heat capacity and density as water.

33

What are the advantages of the Coffee-Cup calorimeter model?

Simple
Inexpensive

34

What are the disadvantages of the Coffee-Cup calorimeter model?

Heat loss to the surroundings

35

What are the advantages of the flame calorimeter?

Simple
Inexpensive

36

What are the disadvantages of the flame calorimeter?

Incomplete combustion
Heat loss to surroundings
Fuel evaporating from the wick

37

What are the advantages of the Bomb calorimeter model?

No heat/ fuel loss
Excess oxygen ensure complete combustion

38

What are the disadvantages of the Bomb calorimeter model?

Expensive

39

Why are enthalpy changes measured from calorimeter less exothermic?

Heat loss to the surroundings
Incomplete combustion of fuel
Evaporation of fuel form he wick

40

Define Rate of Reaction

change in concentration of a reactant or product in a given time

41

How do you calculate the rate of reaction?

Change in concentration/ time

42

What four factors affect the rate of a chemical reaction?

.Concentration (or pressure when reactants are gases)
.Temperature
.Use of a catalyst
.Surface area of a solid reactant

43

What are the three key points of the collision theory ?

Reactions occur when:
.reactant particles collide
.in the correct orientation
.with energy greater than or equal to the activation energy, Ea.

44

Are all collisions successful?

no

45

A successful collision results in what?

A reaction

46

What increases the rate of reaction?

.Increasing collision frequency
.Increasing number of particles with energy greater than or equal to the Activation Energy.

47

How does increasing the concentration/ pressure of gas increase rate of reaction?

-more reactant particles in the same volume
-increased collision frequency
-so reaction rate increases

48

How does increasing surface area increase rate if reaction?

-more particles are exposed for collision
-increased collision frequency
-so reaction rate increases

49

How does increasing the temperature increase the rate of reaction?

-the reactants particles gain kinetic energy and move faster
-increased collision frequency and more particles have energy equal to or greater than the activation energy
-so reaction rate increases

50

How does adding a catalyst increase reaction rate?

-provides an alternative pathway with a lower activation energy
-more particles have energy equal to or greater than the activation energy
-so reaction rates increases

51

What two things can be monitored to judge the rate of reaction?

-A decrease in reactant concentration
-A increase in product concentration

52

What does a progress curve tell us?

The gradient of the curve tells us the rate of the reaction

53

How it initial rate of reaction calculated?

The gradient of a tangent to the graph.

54

Define Catalyst

A substance that increases the rate of reaction without undergoing permanent change. By providing an alternative reaction pathway with a lower activation energy.

55

What is a homogeneous catalyst?

A catalyst in the same physical state as the reactant

56

What does a homogeneous catalyst form with the reactants?

A intermediate compound with the reactants

57

Give an example of a homogenous catalyst

The breakdown of ozone to oxygen by chlorine radicals

58

what is a heterogeneous catalyst?

A catalyst that is in a different state to the reactant

59

How to heterogeneous catalysts interact with the reactant?

Catalysts, usually solid, provides a surface area for the reaction to take place on.

60

Give an example of a heterogeneous catalyst?

Pt/Rn in catalytic converters in cars.

61

How do heterogeneous catalysts work?

Reactant molecules are adsorbed onto the surface of the catalyst, after the reaction has taken place they are desorbed.

62

What is the catalyst used in the Haber process?

Fe (s)

63

What is the equation of the Haber Process?

N2(g) + 3H2 (g) = 2NH3 (g)

64

What is the catalyst used in Reforming?

Pt (s) or Rh(s)

65

What is the equation for Reforming?

C6H14 (g) = C12(g) + H2 (g)

66

What is the catalyst for the Hydrogenation of alkenes?

Ni (s)

67

What is the catalyst for making sulphur trioxide from sulphuric acid?

V2O5

68

What are the 5 reasons catalysts are used in industry?

1. Speed up rate of reaction and offer an alternative route
2.Lower temperature and pressure can be used reducing energy cost.
3.Using less electricity, means less finite resources are used.
4.Reduction in C02 emissions and other pollutants
5. Better atom economy and less waste

69

What is the y- axis labelled on the Maxwell-Boltzman Distribution curve?

Number of molecules with a given energy

70

What is the x - axis labelled on the Maxwell-Boltzman Distribution curve?

Energy

71

How does increasing the temperature of a reaction effect the shape of the Maxwell-Boltzman Distribution curve?

Peak shifts lower and to the right, as a greater proportion of molecules have energy greater than or equal to the Activation Energy, Ea.

72

How does decreasing the temperature of a reaction effect the shape of the Maxwell-Boltzman Distribution curve?

Peak shifts higher and to the left, as a smaller proportion of molecules have energy greater than or equal to the Activation Energy, Ea.

73

What state does the reaction have to take place in to be able to be represented in the Maxwell-Boltzman Distribution curve?

Gas or Liquid

74

Define Dynamic Equilibrium

The rate of the forward and backward reactions are equal in a closed system. The concentrations of reactants and products remain constant (BUT NOT EQUAL)

75

What is the position of equilibrium?

It describes the composition of the equilibrium mixture.

76

What is Le Chatelier's Principle?

When a system is in equilibrium, the position of equilibrium will shift in order to minimise the effect of any external changes and to restore equilibrium.

77

What 3 changes effect the Position of Equilibrium?

1. Temperature
2. Concentration
3. Pressure of reacting gases

78

How does an increase in concentration of reactant effect the position of equilibrium?

Shifts to the product side

79

How does an increase in concentration of product effect the position of equilibrium?

Shifts to the reactant side

80

How does an increase in pressure effect the position of equilibrium?

Shifts to the side with least number of moles

81

How does an increase in temperature effect the position of equilibrium?

Shifts to the endothermic side

82

How does adding a catalyst effect the position of equilibrium?

NO CHANGE

83

What is the EXAM TECHNIQUE for answering position of equilibrium questions?

State the effect the change has on the position of equilibrium AND the effect this has on the yield of products and/or reactants.

84

What are the ideal conditions for the Haber process?

Very High Pressure
Low Temperature

85

Why can the ideal condition for the Haber Process not be met in industry ?

High Pressure is costly with safety implications
Reactions are slow at a low temperature

86

What are the actual conditions for the Haber Process?

.450/500 degrees // 200 atm // Fe Catalyst
.Ammonia is removed as soon as its made
.Unreacted reactants and recycled

87

Define the Equilibrium Constant, Kc

A measure of the position of equilibrium. The magnitude of Kc indicates if there are more reactants or more products in an equilibrium system.

88

What is the general equation for the Equilibrium expression?

aA+bB = cC+dD

89

Is Kc '[reactants] over [products]' or '[products] over [reactants]'?

[Products] over [Reactants]

90

What are square brackets shorthand for?

Concentration

91

If Kc = 1 where does the position of equilibrium lie?

Halfway between the reactants and products ([Reactants] = [Products])

92

If Kc is greater than 1 where does the position of equilibrium lie?

The P of E lies to the right ([Products] is greater than [Reactants])

93

If Kc is less than 1 where does the position of equilibrium lie?

The P of E lies to the left ([Products] is less than [Reactants])

94

Kc only changes with what?

Temperature