Chapter 9

Question 1

What is enthalpy change?

Answer 1

A measure of the heat energy in the a chemical system

Question 2

How is enthalpy change calculated?

Answer 2

The difference in the enthalpies of products - the difference in enthalpies of the reactants.

Question 3

If the energy transfer goes from the system to the surroundings, what sort reaction is it?

Answer 3

An exothermic reaction

Question 4

If energy change goes from the surroundings to the system, what is the reaction?

Answer 4

Endothermic

Question 5

What is the standard conditions for standard enthalpy changes? (Pressure, temperature, concentration, state)

Answer 5

101kPa
298K
1moldm^3
State - physical state of a substance under standard conditions

Question 6

What is the definition of the standard enthalpy change of formation?

Answer 6

The 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 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, with all the reactants and products in their standard states.

Question 8

What is the definition of the enthalpy change of neutralisation?

Answer 8

The energy 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 9

What equations are used to calculate the enthalpy change?

Answer 9

q=mc(delta)T
Mol=mass/Mr

Question 10

What could cause inaccuracies in the experimentally enthalpy change of combustion?

Answer 10

• heat lost to the surroundings other than water
• incomplete combustion may have taken place (seen as soot)
• the alcohol used in the experiment may have evaporated as it is volatile
• The condition of the experiment are unlikely to be identical to standard conditions

Question 11

How could you limit the inaccuracy of the experimental value of the enthalpy of combustion?

Answer 11

Use of drought screens and an input of oxygen gas could minimise hear loss and incomplete combustion

Question 12

What is the definition of the standard enthalpy change of reaction?

Answer 12

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