20 Practice Questions for Year 11 Chemistry Module 4: Drivers of Reactions

Question 6

Considering Reaction A and Reaction B in the diagram below, explain the implications of its activation energy on its reactivity. (3 marks)

Image sourced from Chegg

(L1.3: construct energy profile diagrams to represent and analyse the enthalpy changes and activation energy associated with a chemical reaction)

Question 7

Using graphs, explain how a catalyst might affect a reaction. (3 marks)

(L1.4: model and analyse the role of catalysts in reactions)

Enthalpy and Hess’s Law 

Question 8

With reference to the law of conservation of energy, explain why the dissociation of ionic substances in aqueous solutions are always endothermic on a molecular level (4 marks)

(L2.1: explain the enthalpy changes in a reaction in terms of breaking and reforming bonds, and relate this to the law of conservation of energy)

Question 9

With reference to the law of conservation of energy, explain the enthalpy changes for the following reactions. (3 marks)(L2.1: explain the enthalpy changes in a reaction in terms of breaking and reforming bonds, and relate this to the law of conservation of energy)

Question 10

Draw an enthalpy diagram to illustrate the formation of carbon dioxide, showing both the direct path and indirect path with arrows labelled with its enthalpies. (3 marks)

(L2.2: investigate Hess’s Law in quantifying the enthalpy change for a stepped reaction using standard enthalpy change data and bond energy data, for example: carbon reacting with oxygen to form carbon dioxide via carbon monoxide)

Question 11

Calculate the reaction enthalpy for the formation of anhydrous aluminium chloride

 

from the following data:

Question sourced from ChemTeam

(L2.2:investigate Hess’s Law in quantifying the enthalpy change for a stepped reaction using standard enthalpy change data and bond energy data, for example: carbon reacting with oxygen to form carbon dioxide via carbon monoxide)

Question 12

The following equations illustrate the commercial production of aqueous nitric acid: 

Calculate the total enthalpy change required for the production of 2 moles of nitric acid. (2 marks)

(L2.3: apply Hess’s Law to simple energy cycles and solve problems to quantify enthalpy changes within reactions, including but not limited to heat of combustion, enthalpy changes involved in photosynthesis, enthalpy changes involved in respiration)

Question 13

Using the following information: 

Calculate the total enthalpy change of photosynthesis and a respiration reaction. (4 marks)

(L2.3: apply Hess’s Law to simple energy cycles and solve problems to quantify enthalpy changes within reactions, including but not limited to enthalpy changes involved in photosynthesis)

Entropy and Gibbs Free Energy 

Question 14

Consider the following statements: 

a) Enthalpy is the measure of the internal and flow of energy between objects

b) The system prefers minimum entropy 

c) The unit of entropy is measured in JK-1

d) Entropy is an energy 

Identify and explain why each statement is either true or false. (4 marks) 

(L3.1: analyse the differences between entropy and enthalpy)

Question 15

A student carried out the following experiment: 

1. Fill a beaker up with 200mL of water 
2. Increase the temperature of the water such that it is boiling 
3. Record observations 

Justify whether this is an appropriate example of a model illustrating increasing entropy. 

(L3.2: use modelling to illustrate entropy changes in reactions)

Question 16

For the following reactions, identify whether it is increasing or decreasing in entropy and explain why. (4 marks)

(L3.3: predict entropy changes from balanced chemical reactions to classify as increasing or decreasing entropy)

Question 17

Using the Gibbs free energy formula, deduce whether the reaction would be spontaneous in situation 1,2, 3 and 4 in the table below. (4 marks)

(L3.4: explain reaction spontaneity using terminology, including: Gibbs free energy, enthalpy, entropy)

Question 18

Given the reaction of diamond converting to graphite is 2C(sdiamond)→2C(s(graphite) determine ∆G at 298 K and determine if this reaction is spontaneous or not. What does ∆G say about the rate of this reaction? (3 marks)

∆H°f(C(s)diamond)=1.9kJ/mol 

S°(C(s)diamond=2.38J/(molK) 

S°(C(s)graphite)=5.74J/(molK)

Question sourced from Chemistry LibreTexts

(L3.5: solve problems using standard references and ??? = ?? ? − ???? (Gibbs free energy formula) to classify reactions as spontaneous or nonspontaneous)

Question 19

Predict and explain whether these reactions would be spontaneous with reference to the Gibbs Free energy formula: (4 marks)

a) Endothermic reaction at high temperatures 

b) Endothermic reaction at low temperatures 

c) Exothermic reaction at high temperatures 

d) Exothermic reaction at low temperatures. 

(L3.6: predict the effect of temperature changes on spontaneity)

Question 20

With reference to the Gibbs Free energy, explain why some reactions that go forward are not considered spontaneous reactions. (4 marks) 

(Q19-20: L3.6: predict the effect of temperature changes on spontaneity)