3.2.1 Enthalpy Change

Question 1

What is enthalpy

Answer 1

Measure of the heat energy in a chemical system

Question 2

Enthalpy change equation

Answer 2

Enthalpy change = enthalpy of products - enthalpy of reactants

Question 3

What does exothermic mean

Answer 3

Negative enthalpy change, energy transferred from system to surroundings, temperature of surroundings increases

Question 4

What does endothermic mean

Answer 4

Positive enthalpy change, energy transferred from surroundings to system, temperature of surroundings decreases

Question 5

Activation energy definition

Answer 5

Minimum energy required for reaction to take place

Question 6

Standard pressure

Answer 6

100kPa

Question 7

Standard temperature

Answer 7

298K (25C)

Question 8

Standard concentration

Answer 8

1 mol dm^-3

Question 9

Standard state

Answer 9

Physical state of substance under standard conditions

Question 10

Standard enthalpy change of reaction

Answer 10

Enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states

Question 11

Standard enthalpy change of formation definition

Answer 11

Enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states

Question 12

Standard enthalpy change of combustion definition

Answer 12

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

Question 13

Standard enthalpy change of neutralisation definition

Answer 13

Enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2O under standard conditions with all reactants and products in their standard states

Question 14

Equation used for energy change

Answer 14

q=mc∆T

Question 15

Average bond enthalpy definition

Answer 15

Energy required to break one mole of a specified type of bond in a gaseous molecule

Question 16

Energy in bond breaking

Answer 16

Energy is required to break bonds, bond breaking is endothermic (+∆H)

Question 17

Energy in bond making

Answer 17

Energy is released when bonds form, bond making is exothermic (-∆H)

Question 18

Enthalpy change equation from average bond enthalpies

Answer 18

Energy required to break bonds - energy released when making bonds = ∆H

Question 19

What is Hess’ law

Answer 19

If a reaction can take place by 2 routes and the starting and finishing conditions are the same, total enthalpy change is the same for each route

Question 20

Enthalpy change of formation equation for Hess’ law

Answer 20

Total enthalpy change of formation of products - total enthalpy change of formation of reactants

Question 21

Enthalpy change of combustion equation for Hess’ law

Answer 21

Total enthalpy change of combustion of reactants - total enthalpy change of combustion of products