9.1 - Enthalpy changes

Question 1

What is enthalpy? H

Answer 1

The heat content that is stored in a chemical system

Question 2

What are the two directions of energy transfer?

Answer 2

1. From the system TO the surroundings - an exothermic change, temperature rise
2. From the surroundings To the system - an endothermic change, temperature fall

Question 3

Draw an enthalpy profile of an exothermic reaction

Answer 3

:)

Question 4

Draw and enthalpy profile of an endothermic reaction

Answer 4

:)

Question 5

What are the standard conditions?

Answer 5

1. Standard pressure, 100KPa
2. Standard temperature, 298K
3. Standard concentration for solutions, 1moldm-3
4. Standard state, the state under standard conditions

Question 6

What is the standard enthalpy change of reaction?

Answer 6

The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions and in their standard states

Question 7

What is the enthalpy change of formation?

Answer 7

The enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions and in their standard states

Question 8

What is the enthalpy change of combustion?

Answer 8

The enthalpy change that takes place when one mole of a substance completely reacts with oxygen under standard conditions and in their standard states

Question 9

What is the enthalpy change of neutralisation?

Answer 9

The energy change that accompanies the reaction of an acid and base to form one mole of H20(l) under standard conditions and in their standard states