chemistry topic 5

Question 1

what happens during an exothermic reaction

Answer 1

An exothermic reaction transfers energy to the surroundings so the temperature of the surroundings increases

Question 2

what happens during an endothermic reaction

Answer 2

An endothermic reaction is one that takes energy from the
surroundings so the temperature of the surroundings decreases

Question 3

give examples of exothermic reactions

Answer 3

• Combustion
• Neutralisation
• Oxidation

Question 4

give examples of endothermic reactions

Answer 4

• Thermal decomposition
• Sports injury packs
• Photosynthesis

Question 5

what has to happen for a chemical reaction to take place

Answer 5

Chemical reactions can only occur when reacting particles collide with each other
with sufficient energy.

Question 6

what is activation energy

Answer 6

The minimum amount of energy that particles must have to react is called the activation energy

Question 7

compare the energy of reactants and products in exothermic reactions

Answer 7

Exothermic reactions
Reactants have MORE energy
than products

Question 8

compare the energy of reactants and products in endothermic reactions

Answer 8

Endothermic reactions
Reactants have LESS energy
than products

Question 9

whats the formula for overall energy change in a chemical reaction

Answer 9

Overall energy change =
Bonds broken – Bonds formed

Overall energy change = reactants - products

Question 10

give definition of exothermic reactions

Answer 10

energy released from forming new bonds is greater than energy needed to break bonds

Question 11

give definition of endothermic reactions

Answer 11

Energy needed to break bonds is
greater than energy released
from forming new bonds

Question 12

describe Exothermic and endothermic reactions - REQUIRED PRACTICAL

Answer 12

1. Add 25cm3 hydrochloric acid to beaker
2. Measure initial temperature of acid
3. Add a metal to acid
4. Measure temperature change
5. Repeat with other metals
6. More reactive metals will have the highest temperature change

Question 13

how do cells in batteries work

Answer 13

Cells contain chemicals which react to produce electricity.

Question 14

what does the voltage produced by a cell depend on

Answer 14

depends on the type of
electrode and electrolyte.

Question 15

what are batteries

Answer 15

Batteries consist of two or more cells connected in series to
provide a greater voltage.

Question 16

how can Rechargeable cells and batteries can be recharged

Answer 16

can be recharged if the chemical reactions are reversed

Question 17

give features of non-rechargeable cells and batteries

Answer 17

-Cheap

-Only be used once

-Expensive in the long run

-Output falls gradually

-Toxic materials released when disposed

Question 18

give features of rechargeable cells and batteries

Answer 18

-Expensive

-Used many times

-Cheap in the long run

-Output stays constant until flat

-Less toxic materials released when disposed

Question 19

what do hydrogen fuel cells involve

Answer 19

hydrogen fuel cells involve the oxidation of hydrogen
to produce water.

Question 20

advantages of using hydrogen fuel cells

Answer 20

Take less time to refuel than to recharge batteries
Can travel further before refuelling
Doesn’t produce toxic chemicals when disposed of
No CO2 produced

Question 21

describe the process that make fuel cells work

Answer 21

Fuel cells work by using the
reaction between hydrogen
and oxygen to produce an
electric current:

1) The hydrogen atom loses
an electron (this is called
“oxidation”)

2) They then pass through
the electrolyte

3) The oxygen atoms gain two
electrons each
(“reduction”).