C5 Energy Changes - Random Revision pages 138 - 140

Question 1

True or False? Chemical reactions change the amount of energy in the universe. Explain your answer?

Answer 1

False. Energy is always conserved in reactions./Energy cannot be created or destroyed

Question 2

Give an example of exothermic chemical reaction?

Answer 2

Any one from: e.g.

Burning fuels/combustion
Neutralisation
Many oxidation reactions

Question 3

How does an exothermic reaction affect the temperature of its surroundings?

Answer 3

It increases the temperature of its surroundings

Question 4

Do the products of an endothermic reaction store more or less energy than reactants? Explain your answer

Answer 4

More, because energy is taken in from the surroundings during the reaction

Question 5

An exothermic reaction is carried out in a polystyrene cup. Give one way to reduce heat loss to the surroundings during this experiment?

Answer 5

Any one from: e.g.

Place the polystyrene cup in a beaker of cotton wool

Put a lid on the polystyrene cup

Question 6

How can you calculate the temperature change of a reaction?

Answer 6

Subtract the starting temperature of the reaction mixture from the final temperature

Question 7

True or False? Breaking bonds is an exothermic process. Explain your answer

Answer 7

False. Energy must be supplied in order to break chemical bonds, so the process is endotheric

Question 8

In the process below exothermic or endothermic? Explain your answer

H CL &raquo_space;»> H + Cl

Answer 8

Endothermic, because bonds are broken (which requires energy)

Question 9

In what type of reaction is the energy released by forming bonds greater than the energy used to break them?

Answer 9

Exothermic

Question 10

How could you use known bond energies to calculate the overall energy change of a reaction?

Answer 10

Add up the bond energies of the reactants, then substract the bond energies of the products