C2.5 Chemical Reactions

Question 1

What is an endothermic reaction?

Answer 1

Endothermic reactions take in heat energy, so they cool down their surroundings.

Question 2

What happens to the bonds in an exothermic reaction?

Answer 2

Energy is released when bonds are made, so exothermic reactions make bonds. Less energy is needed to break the bonds of the reactants so more energy is released when the bonds are made.

Question 3

What happens to the bonds in an endothermic reaction?

Answer 3

More energy is needed to break the bonds in the reactants than is released in making the bonds of the products. So energy increases.

Question 4

How does temperature increase reaction rate?

Answer 4

The higher the temperature of the reactants the faster the reaction. This is because the higher the temperature the more energy the particles have, so the faster they move which increases the chance of successful collisions and therefore the rate of reaction.

Question 5

How does concentration increase the rate of reaction?

Answer 5

The more concentrated a solution, the more solute particles there are. This means that collisions are more likely so the rate of reaction will increase.

Question 6

How does the surface area increase the rate of reaction?

Answer 6

Only the particles on the edge of a solid can take place in a reaction, so if the surface area is greater there will be more frequent collisions and a higher rate of reaction.

Question 7

What are catalysts?

Answer 7

Catalysts are substances that speed up chemical reactions without being sued up in the reactions.

Question 8

How do catalytic converters work?

Answer 8

Catalytic converters reduce the pollutants released by cars. They help to combine carbon monoxide and unburned petrol with oxygen to form carbon dioxide and water vapour.

Question 9

How are catalytic converters suited to their job?

Answer 9

• Contain transition metals platinum, rhodium or palladium, all of which speed up reactions which remove the pollutants in the exhaust gases.
• The metals used are very expensive, so to make the converter as efficient as possible without using too much of the metals, catalytic converts have a high surface area to volume ratio.
• Catalytic converters work best at high temperatures.

Question 10

What is an exothermic reaction?

Answer 10

Exothermic reactions give out what energy. This increase the temperature of the reactants and the surroundings increases.