U3-3-2 - Enthalpy of Combustion

Question 1

What is E_h?

Answer 1

Heat energy (in kJ)

Question 2

What is c?

Answer 2

Specific heat capacity of water (4.18)

Question 3

What is ∆T?

Answer 3

Change in temperature

Difference between starting and final temperature of water

Question 4

What is m?

Answer 4

Mass of substance heated, in kg
(NOT mass of fuel!)

For water, 1000 cm³ = 1 kg

Question 5

Suggest the greatest source of error in this experiment

Answer 5

Heat loss to surroundings

due to lack of heat shield

Question 6

Suggest a piece of apparatus that can minimise heat loss to surroundings during combustion

Answer 6

Heat shield (or bomb calorimeter)

Question 7

The energy released when 1 mole of a substance undergoes complete combustion.

Answer 7

Enthalpy of combustion

Question 8

Ethanol has GFM = 46 g.

Burning 4.6 g released 136.7 kJ.

Write an expression to calculate the enthalpy of combustion for ethanol.

Answer 8

Use proportion to scale up energy to 1 mole of fuel

1 mole has mass = GFM

Question 9

This equation does not represent the enthalpy of combustion. Why?

Answer 9

Must be complete combustion (products CO₂ and H₂O)

Question 10

Enthalpy of combustion

Answer 10

The energy released when 1 mole of a substance undergoes complete combustion.