Topic 8 - ENERGETICS

Question 1

What is the definition of standard enthalpy of formation?

Answer 1

The enthalpy change when:
- One mole of a substance
- is formed from its elements
- in their standard states (at 298K and 100kPa)

Question 2

What is the definition of standard enthalpy of combustion?

Answer 2

The enthalpy change when:
- One mole of a substance
- is completely oxidised in excess oxygen
- at standard conditions (298K and 100kPa)

Question 3

What is the definition of standard enthalpy of neutralisation?

Answer 3

The enthalpy change when:
- One mole of water forms
- By the neutralisation of an acid and alkali
- At standard conditions (298K and 100kPa)

Question 4

What is the formula for heat energy produced (Q)?

Answer 4

Q=mc∆T
where:
m = mass
c = specific heat capacity
∆T = change in temperature

Question 5

What is the formula for enthalpy of a reaction?

Answer 5

∆H=-Q/moles

Question 6

What are the two main errors that occur during calorimetry?

Answer 6

• Heat energy is lost to surroundings
• Less energy is released

Question 7

What is the effect if heat energy is lost during calorimetry?

Answer 7

• ∆T would be less positive
• Q would be less positive
• ∆H would be less negative

Question 8

What is the effect if less energy is released during calorimetry?

Answer 8

∆T would be less positive
- Q would be less positive
- ∆H would be less negative

Question 9

What is Hess’ Law?

Answer 9

∆H for a reaction is independent of the route taken

Question 10

What are the 4 possible reactions when calculating Hess’ Law?

Answer 10

• Enthalpy of formation
• Enthalpy of combustion
• Enthalpy of neutralisation
• Dissolving