Module 3 - Energy

Question 0

Exothermic

Answer 0

A reaction in which the enthalpy change of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings.

Question 1

Enthalpy, H

Answer 1

The heat content that is stored in a chemical system.

Question 2

Endothermic

Answer 2

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

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

Activation energy

Answer 4

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

Question 5

Standard conditions

Answer 5

S pressures of 100 kPa (1 atmosphere) and a stated temperature, usually 298K, and a concentration of 1.0 mol dm^-3 (for reactions with aqueous solutions).

Question 6

Standard state

Answer 6

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

Question 7

Standard enthalpy change of reaction

Answer 7

The enthalpy change that accompanies a few action in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.

Question 8

Standard enthalpy change of combustion

Answer 8

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 9

Standard enthalpy change of formation

Answer 9

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 10

Unit for enthalpy changes

Answer 10

kJ mol^-1

Question 11

Specific heat capacity, c

Answer 11

The nergy required to raise the temperature of 1g of a substance by 1 degree Celsius.

Question 12

Bond enthalpy

Answer 12

The enthalpy change that takes place when breaking by homolytic fission 1 mole of a give bond in the molecules of a gaseous species.

Question 13

Average bond enthalpy

Answer 13

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 14

Hess’ law

Answer 14

‘If a reaction can take place by more than none route and the initial and final conditions are the same, the total enthalpy change is the same for each route.’

Question 15

Enthalpy cycle

Answer 15

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 16

Rate of reaction

Answer 16

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

Question 17

Heterogenous catalysis

Answer 17

A catalysis of a reaction in which the catalyst has a different physical state from the reactants; frequently, the reactants ate gases whilst the catalyst is a solid.

Question 18

Homogenous catalysis

Answer 18

A catalysis of a reaction in which the catalysts and reactants are in the same physical stage, which is most frequently the aqueous or gaseous state.

Question 19

Dynamic equilibrium

Answer 19

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

Question 20

Le Chatelier’s principle

Answer 20

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