C7 - energy changes

Question 1

What is the difference between an endothermic and exothermic reaction

Answer 1

Endothermic energy is absorbed, exothermic energy is released

Question 2

What causes more or less energy to be released in a displacement reaction

Answer 2

The gap in reactivity between the reactants

Question 3

How do you calculate heat transferred in a reaction (using water)

Answer 3

Heat energy = mass of water (g) x specific heat capacity of water (4.2g/oC) x temperature rise

Question 4

Why do exothermic reactions release energy

Answer 4

The bonds made release more energy than the bonds broken needed to be broken

Question 5

Why do endothermic reactions absorb energy

Answer 5

The bonds broken require more energy to break than the bonds made release

Question 6

Does making bonds release or require energy

Answer 6

Release

Question 7

What happens when two metals are played in solution and connected by a wire

Answer 7

There is a potential difference between them - bigger gap in reactivity means bigger voltage

Question 8

What is electrochemistry (two metals in solution connected by a wire producing a voltage) used for

Answer 8

Batteries

Question 9

What is a primary cell

Answer 9

A cell that cannot be recharged

Question 10

What is the equation in a hydrogen fuel cell at the anode

Answer 10

2H2 goes to 4H+ + 4e-

Question 11

What is the equation in a hydrogen fuel cell at the cathode (after hydrogen ions have gone through electrolyte solution)

Answer 11

O2 + 4H+ + 4e- goes to 4H2O