Energy Changes

Question 1

what happens in an exothermic reaction?

Answer 1

there is a transfer of energy to surroundings which registers as a temperature increase

Question 2

what happens in an endothermic reaction?

Answer 2

there is a transfer of energy from the surroundings which registers as a temperature decrease

Question 3

what is the overall energy change for a reaction also known as?

Answer 3

delta H or enthalpy change

Question 4

when is a reaction exothermic?

Answer 4

energy required to break bonds in reactants is lower than energy given out when new bonds are formed

Question 5

when is a reaction endothermic?

Answer 5

energy required to break bonds in reactants is higher than energy given out when new bonds are formed

Question 6

is breaking bonds exothermic or endothermic?

Answer 6

endothermic

Question 7

is forming bonds exothermic or endothermic?

Answer 7

exothermic

Question 8

how do you calculate delta H?

Answer 8

bonds to break - bonds formed

Question 9

what does a negative value for delta H mean?

Answer 9

the reaction is exothermic

Question 10

how do chemical cells work?

Answer 10

contain chemicals which react to produce electricity

Question 11

what factors affect voltage in chemical cells?

Answer 11

• identity of metals; bigger difference in reactivity = bigger voltage
• electrolyte; identity and concentration

Question 12

what is a battery?

Answer 12

2 or more cells connected

Question 13

how do you make a 6V battery?

Answer 13

4 1.5V cells in series

Question 14

which electrode is more reactive in chemical cells?

Answer 14

the anode

Question 15

what are the 3 types of cell?

Answer 15

normal (chemical) cell
hydrogen fuel cell
rechargeable cell

Question 16

how do normal cells work?

Answer 16

go flat as chemicals used up

Question 17

how do hydrogen fuel cells work?

Answer 17

chemicals pumped in to replace those used up

Question 18

how do rechargeable cells work?

Answer 18

chemical reactions reverse to reproduce chemicals used up

Question 19

what is the chemical reaction in a hydrogen fuel cell?

Answer 19

hydrogen (fuel) reacts with pure oxygen or air

Question 20

what is the product of the reaction in a fuel cell?

Answer 20

water

Question 21

what are 2 positives of hydrogen fuel cells?

Answer 21

• produce electricity as long as hydrogen is provided
• do not get less efficient

Question 22

what are 2 negatives of hydrogen fuel cells?

Answer 22

• hydrogen gas is explosive and difficult to store safely
• produce low voltages so many are required

Question 23

what are 2 negatives of rechargeable battery cells?

Answer 23

• will run out and need recharging
• store less electricity over time

Question 24

what are 2 positives of rechargeable battery cells?

Answer 24

• no dangerous fuel required
• produce greater voltages compared to hydrogen fuel cells

Question 25

Explain the difference between the processes in electrolysis and in a chemical cell.

Answer 25

electrolysis uses electricity to produce a chemical reaction BUT cells use a chemical reaction to produce electricity