2.3

Question 1

What is exothermic?

Answer 1

Refers to a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat lost to the surroundings.

Question 2

What is endothermic?

Answer 2

Refers to a reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings.

Question 3

What is an enthalpy profile diagram?

Answer 3

A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products.

Question 4

What is activation energy?

Answer 4

The minimum energy required to start a reaction by the breaking of bonds.

Question 5

What are standard conditions?

Answer 5

A pressure of 100kPa, a stated pressure of 298 Kelvin and a concentration of 1 mol dm⁻³ for reactions with aqueous solutions.

Question 6

What is standard state?

Answer 6

The physical state of a substance under the standard conditions of 100kPa and 298 K.

Question 7

What is the standard enthalpy change of combustion?

Answer 7

The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states.

Question 8

What is the standard enthalpy change of formation?

Answer 8

Of a compound is the enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.

Question 9

What is specific heat capacity?

Answer 9

The energy required to raise the temperature of 1g of a substance by 1⁰C.

Question 10

What is bond enthalpy?

Answer 10

The enthalpy change that take place when breaking, by homolytic fission, 1 mol of a given bond in the molecules of a gaseous species.

Question 11

What is average bond enthalpy?

Answer 11

The average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species.

Question 12

What does Hess’ law state?

Answer 12

If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.

Question 13

What is an enthalpy cycle?

Answer 13

A diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess’ law.

Question 14

What is the rate of reaction?

Answer 14

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

Question 15

What is heterogenous catalysis?

Answer 15

Catalysis of a reaction in which the catalyst has a different physical state from the reactants.

Question 16

What is homogenous catalysis?

Answer 16

Catalysis of a reaction in which the catalyst and reactants are in the same physical state.

Question 17

What is the Boltzmann distribution?

Answer 17

The distribution of energies of molecules at a particular temperature, often shown as a graph.

Question 18

What is dynamic equilibrium?

Answer 18

The equilibrium that exists in a closed system when the rate of forward reaction is equal to the rate of the reverse reaction.

Question 19

What does le Chatelier’s principle state?

Answer 19

That when a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change.

Question 20

What is enthalpy?

Answer 20

The heat content that is stored in a chemical system.