Topic 8

Question 1

Enthalpy change define it

Answer 1

Enthalpy change is the energy change in a reaction at constant pressure
The measurements were made under standard conditions and the elements were in their standard states

Question 2

Standard conditions

Answer 2

100 kPa or 1ATM pressure

298k

Question 3

Exothermic reaction

Answer 3

Gives out heat energy
Temperature goes up
Negative enthalpy change

Question 4

Endothermic reactions

Answer 4

Takes in heat energy
Temperature falls
Positive enthalpy change

Question 5

Standard enthalpy change of reaction

Answer 5

Enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation under standard conditions

Question 6

Change of formation

Answer 6

Enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions

Question 7

Change of combustion

Answer 7

Enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions

Question 8

Change of neutralisation

Answer 8

Enthalpy change when an acid and alkali react together under standard conditions to form one mole of water

Question 9

Formula for energy change

Answer 9

Q equals MC Delta T

Question 10

Hesses law

Answer 10

The total enthalpy change of reaction is always the same no matter which route is taken

Question 11

Breaking bonds requires

Answer 11

Energy

So bond breaking is endothermic

Question 12

Forming bonds

Answer 12

Releases energy

So bond forming is exothermic

Question 13

Bond energy

Answer 13

The amount of energy required to break one mole of the type of bond in a molecule in the gas phase