3.1.4 - Energetics

Question 1

Define ‘enthalpy’

Answer 1

A measure of heat content of a substance

Question 2

Define ‘enthalpy change’

Answer 2

Change in heat content of a substance at constant pressure

Question 3

What are standard conditions?

Answer 3

100kPa, 298K

Question 4

What is ‘standard enthalpy change of a reaction’/’enthalpy of a reaction’?

Answer 4

The enthalpy change for a reaction with the quantities quoted in the equation

Question 5

Define ‘standard enthalpy change of formation’

Answer 5

Enthalpy change when one mole of a substance is formed from its constituent elements with all reactants and products in standard states under standard conditions

Question 6

Define ‘standard enthalpy change of combustion’

Answer 6

Enthalpy change when one mole of a substance is completely burned in oxygen with all reactants and products in standard states under standard conditions

Question 7

Define ‘standard enthalpy change of neutralisation’

Answer 7

Enthalpy change when one mole of water is formed in a reaction between an acid and an alkali under standard conditions

Question 8

How do you find the amount of heat energy given out/absorbed?

Answer 8

q = mcΔT
q - energy change (J)
m - mass of substance (usually water) heated (g)
c - SHC of substance heated (usually 4.18 [water])
ΔT - temperature change of substance heated (K)

Question 9

How do you calculate enthalpy change once you have found the overall energy change?

Answer 9

q/1000 = answ in kJ

Then kJ/moles = xxxx kJ mol^-1

Question 10

What is Hess’s Law?

Answer 10

The enthalpy change for a reaction is independent of the route taken

Question 11

Enthalpy change = ______ - _________

Answer 11

Enthalpy change = sum of enthalpy of products - sum of enthalpy of reactants

Question 12

What is the enthalpy of formation for an element?

Answer 12

Zero

Question 13

Define ‘bond enthalpy’

Answer 13

The enthalpy change required to break one mole of covalent bonds in the gas phase