Unit 2-Energy from fuels

Question 1

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

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

A spirit burner was filled with ethanol (C₂H₅OH) and used to heat a copper can containing 200 cm^₃ of water. The temperature of the water rose from 22˚C to 27˚C.

Calculate the heat energy released from this combustion of ethanol.

Answer 6

Eh=cmΔT

Eh=4.18 x 0.2 x 5

=4.18kJ

Question 7

Different fuels provide different quantities of energy. Describe how this can be determined experimentally.

Answer 7

Question 8

his setup can be used to determine the energy released when an alcohol (alkanol) is burned.

Suggest one improvement to the investigation.

Answer 8

Any one from:

• heat insulation
• repeat to get average
• move burner nearer to can
• remove tripod and clamp can
• stir water
• thermometer not touching copper