C5 energy changes

Question 1

what is the conservation of energy rule

Answer 1

Energy is not created or destroyed, only transferred. The total amount of energy in the universe stays the same.

if a reaction transfers energy to the surroundings the product molecules must have less energy than the reactants by the amount transferred

Question 2

what is an exothermic reaction

Answer 2

a reaction that transfers energy to the surroundings

Question 3

name 2 features of exothermic reactions

Give two examples

Answer 3

-temperature of surroundings increases
-product molecules must have less energy than the reactants by the amount transferred

Combustion, neutralisation reaction.

Question 4

what’s an endothermic reaction

Answer 4

a reaction that takes in energy from the surroundings so the temperature of the surroundings decreases

Question 5

what are 2 features of an endothermic reaction

Give an example of a use of an endothermic reaction.

Answer 5

-temperature of surroundings decreases
-product molecules must have more energy than reactants

For example sports injury packs.

Question 6

what is activation energy

Answer 6

minimum amount of energy that particles that need to have to react

Difference in energy between the energy of the reactants and the highest point in the reaction profile.

Question 7

why must energy be supplied in reactions

Answer 7

to break down the bonds of the reactants

Question 8

how do you calculate overall energy change

Answer 8

sum of energy taken in to break bonds - sum of energy released to form bonds

Question 9

what are cells

Answer 9

they contain chemicals which react to produce electricity

Question 10

how can a simple cell be made

Answer 10

connecting two different metals in contact with an electrolyte

Question 11

what is a battery

Answer 11

two or more cells together to grant a greater voltage

Question 12

explain non rechargeable batteries

Answer 12

-chemical reactions stop when one of the reactants has been used up
-alkaline batteries are always non-rechargeable

Question 13

explain rechargeable batteries

Answer 13

chemical reactions are reversed when an external electrical current is supplied

Question 14

what are some advantages of hydrogen fuel cells

what about disadvantages?

Answer 14

Advantages:
-can be used constantly provided fuel is supplied.
-only produces water when burnt (no greenhouse gas emissions)

Disadvantages:
-hydrogen gas needs to be stored at high pressure and is difficult to transport

Question 15

What are some advantages of rechargeable cells/batteries?

What about disadvantages?

Answer 15

Advantages:
-Can be recharged using electricity so fuel does not have to be supplied.

Disadvantages:
-Hard to dispose of (non-biodegradeable)
-Will eventually stop working

Question 16

what is the half equation for a hydrogen fuel cell at the cathode

Answer 16

H2(g) -> 2e- + 2H+(aq)

Question 17

what is the half equation for a hydrogen fuel cell at the anode

Answer 17

4H+(aq) + O2(g) + 4e- -> 2H2O(g)=