Unit 2-Energy From Fuels
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What is an exothermic reaction?
A reaction that releases heat energy.
What is an endothermic reaction?
A reaction that takes in heat energy.
What type of reaction is combustion?
Exothermic
What is a fuel?
A substance that burns to release energy.
What is the word equation for complete combustion of hydrocarbons?
Hydrocarbon + oxygen → carbon dioxide + water
What is the word equation for incomplete combustion of hydrocarbons?
Hydrocarbon + oxygen → carbon monoxide + water (+ soot).
Why is incomplete combustion dangerous?
It produces carbon monoxide, a toxic gas.
What equation is used to calculate heat energy released?
Eh = c x m x ΔT
What does Eh mean?
Heat energy released (kJ)
What does c mean?
Specific heat capacity of the substance being heated.
What is the specific heat capacity of water?
4.18 kJ kg-1 oC-1
What does m mean?
Mass of the substance being heated (kg)
What does ΔT mean?
Change in temperature (oC).
How can the energy released by a fuel be determined experimentally?
Burn the fuel to heat a known mass of water and measure the temperature rise.
Why use a draught shield in a fuel‑burning experiment?
To reduce heat loss to the surroundings.
Why move the burner closer to the can?
To reduce heat loss and transfer more heat to the water.
Why remove the tripod and clamp the can instead?
To reduce heat loss and allow more efficient heating.
Why stir the water during heating?
To ensure even heating and a more accurate temperature reading.
Why must the thermometer not touch the metal can?
To avoid measuring the temperature of the metal instead of the water.
Why repeat the experiment and take an average?
To improve reliability and reduce the effect of anomalies.