Unit 2 - Energy from Fuels

Question 1

What name is given to any chemical reaction which releases energy?

Can you give an example related to fuels?

Answer 1

Exothermic.

Combustion reactions are exothermic reactions.

Question 2

What is the equation for the complete combustion of hydrocarbons?

Answer 2

Hydrocarbon + oxygen –> Carbon dioxide + Water

Question 3

What is the equation for the incomplete combustion of hydrocarbons?

Answer 3

Hydrocarbon + oxygen –> Carbon monoxide + Water ( +Soot)

Question 4

What equation is used to calculate the energy released by burning a fuel?

Answer 4

Eh=cmΔT

Question 5

In the equation Eh=cmΔT, what does each term mean?

Answer 5

Eh is the heat energy released (in kJ or kJ mol-1)

c is the specific heat capacity of water. It is a constant, 4.18 kJ kg-1 ˚C-1

m is is the mass of water (in kg) (100cm3 = 0.1kg)

ΔT is the change in temperature (˚C)

Question 6

What is the test for water and what result shows water is present?

Answer 6

Cobalt Chloride Paper

Turns from blue to pink if water is present

Question 7

What is the test for Carbon Dioxide and what result shows it is present?

Answer 7

Limewater

Turns from clear to cloudy if CO2 is present