Nature’s Chemistry #3: Energy From Fuels

Question 1

Why are alkanes and alcohols excellent fuels?

Answer 1

They release vast amounts of energy when they undergo combustion

Question 2

Combustion of alkanes
Alkane + oxygen ->

Answer 2

Carbon dioxide + water

Question 3

Combustion of alkenes
Alkene+ oxygen ->

Answer 3

Carbon dioxide + water

Question 4

Combustion of cyclohexanes
Cyclohexane + oxygen ->

Answer 4

Carbon dioxide + warwr

Question 5

What makes some fuels better than others?

Answer 5

They release more energy during combustion reactions

Question 6

Negative sign

Answer 6

Exothermix

Question 7

No sign (positive)

Answer 7

Endothermic

Question 8

Eh = cm Δt

Answer 8

Eh = energy released /kJ
c = specific heat capacity of the water /4.18kJ kg-1 °C-1
m = mass of water heated /kg
** Δt** = temperature change / °C

Question 9

As well as water, what can heat be absorbed by?

Answer 9

Other substances

Question 10

What happens if a Eh=cm Δt uses a substance other than water?

Answer 10

• This equation is still used, but c will not be 4.18
• the specific heat capacity of the substance being heated will be given in the question

Question 11

What can more accurate values of the energy released when fuels undergo combustion be obtained using?

Answer 11

A bomb calorimeter

Question 12

The design of the bomb calorimeter:

Answer 12

• reduces heat loss to the surroundings
• reduces incomplete combustion

Question 13

How might an energy from fuels experiment be made more accurate?

Answer 13

• a metal can for conductivity
• draught shield to reduce energy lost to surroundings