Paper 1 - Topic 5, Energy Changes

Question 1

What is the activation energy

Answer 1

The minimum amount of energy for particles to collide with in order for a successful reaction to occur

Question 2

What are alkaline batteries

Answer 2

They are non-rechargeable and the chemical reactions stop once one of the reactants has been used up

Question 3

What is a battery

Answer 3

Two or more cells connected together in series to provide a greater voltage

Question 4

What are chemical cells

Answer 4

Cells containing chemicals which react tot produce elctricity

Question 5

What is an endothermic reaction

Answer 5

A reaction that takes in energy from the surroundings, so the temp of the surroundings decreases

Question 6

What happens in an endothermic reaction

Answer 6

Energy needed to break existing bonds us greater than the energy released from forming new bonds

Question 7

What is an exothermic reaction

Answer 7

A reaction where energy is transferred to the surroundings, so the temp of the surroundings increases

Question 8

What happens in an exothermic reaction

Answer 8

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

Question 9

What is the overall energy change of a reaction

Answer 9

The difference between the sun of the energy needed to break the bonds and the sum of the energy released when bonds in the products are formed

Question 10

What is the reaction profile

Answer 10

Reaction profiles are used to show the relative energies of reactants and product, the activation energy and the overall energy change of a reaction

Question 11

Why can rechargeable cells be recharged

Answer 11

Because the chemical reactions are reversed when an external electrical current is supplied

Question 12

What is the conservation of energy principle

Answer 12

Energy is conserved in chemical reactions. The amount of energy in the universe at the end of a chemical reaction is the same as before the reaction took place

Question 13

What are some examples of exothermic reactions

Answer 13

-combustion, oxidation reactions and self-heating cans and hand warmers

Question 14

What are some examples of endothermic reactions

Answer 14

• thermal decomposition
• reaction of citric acid
• sports injury packs

Question 15

What occurs in a chemical reaction in terms of bond energies p? Describe exothermic and endothermic reactions in terms of bond breaking and forming

Answer 15

• energy is supplies to break bonds and energy is released when bonds are made
• exothermic: energy released from forming bonds is greater than that needed to break bonds
• endothermic: energy needed to break bonds is greater than energy released when making them

Question 16

What is the equation to find enthalpy change in terms of bond energies

Answer 16

Energy of reaction = sum of bonds broken - sum of bonds made

Question 17

What is a cell

Answer 17

A cell is composed of two electrodes dipped in an electrolyte solution and produces energy to form a chemical reaction

Question 18

What determines the voltage obtained from a cell

Answer 18

Identities of metals used as electrodes and the identity and concentration of an electrolyte

Question 19

State the advantages and disadvantages of using cells and batteries

Answer 19

+ more or less cheap, some are rechargeable, convenient source of electrical energy
- harmful chemicals

Question 20

What is a fuel cell

Answer 20

Fuel cells are supplied by fuel and oxygen to oxidise the fuel to generate electricity

Question 21

What is the overall reaction in a hydrogen fuel cell, what are the half equations

Answer 21

Cathode: 2H₂ —> 4H ⁺ + 4e ^-
Anode: O ₂ + 4H ⁺ + 4e ^- —> 2H ₂O
Overall: 2H ₂ + O ₂ —> 2H ₂O

Question 22

What are the advantages and disadvantages of hydrogen fuel cells

Answer 22

+ no pollutants, no recharging
- flammable, H ₂ difficult to store, toxic chemicals, expensive production of H ₂ by electrolysis