Energy Changes (P1)

Question 1

Exothermic vs endothermic

Answer 1

Exo gives out heat

Endo takes in heat

Question 2

Reaction profile for endothermic

Answer 2

Increases a lot to the activation energy and decreases a bit to the products energy

Question 3

Reaction profile for exothermic

Answer 3

Increases a bit to activation energy, decreases a lot to product energy

Question 4

When is energy taken in and absorbed in relation to bonds?

Answer 4

Taken in to break, released when made

Question 5

Electrical cell

Answer 5

Two conductive metals in an electrolyte (solution with ions)
Electrodes are connected by a wire to let charge flow
(Electrolysis)

Question 6

When is the p.d. of a cell greatest?

Answer 6

When the electrodes have the greatest difference in reactivity

Question 7

Hydrogen fuel cells

Answer 7

Electrolyte is acid
Hydrogen makes h+ which cross the acid and the e- go through the wire
They then become hydrogen again
Each reacts with 2 oxygen atoms to make water
Releases oxygen and heat

Question 8

Why does breaking bonds release energy

Answer 8

Because the elements are more stable

Question 9

How to calculate energy change?

Answer 9

Reactants-products

Multiply by subscript but not moles

Question 10

Hydrogen fuel cell negative electrode

Answer 10

2H2 —> 4H+ +4e-

Question 11

Hydrogen fuel cell positive electrode

Answer 11

O2 + 4H+ + 4e- —> 2H2O

Question 12

Overall hydrogen fuel cell reaction

Answer 12

2H2 + O2 —> 2H2O

Question 13

Hydrogen fuel cell advantages vs rechargeable

Answer 13

Produce electricity until hydrogen runs out, rechargeables need recharging
Hydrogen maintains efficiency, rechargeables are less after each charging cycle
Water produced can be useful

Question 14

Hydrogen fuel cell disadvantage vs rechargeable

Answer 14

Hydrogen is explosive, rechargeables cannot explode unless badly made
Rechargeables produce a higher p.d., you need several hydrogen fuel cells

Question 15

Endothermic examples

Answer 15

Boiling
Melting
Evaporating
Photosynthesis

Question 16

Exothermic examples

Answer 16

Freezing
Condensing
Combustion
Respiration
Neutralisation