Paper 1 - energy changes

Question 1

Activation energy

Answer 1

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

Question 2

*Alkaline batteries

Answer 2

Alkaline batteries are non-rechargeable. In non-rechargeable cells and
batteries the chemical reactions stop when one of the reactants has been used up.

Question 3

*Battery:

Answer 3

: Batteries consist of two or more cells connected together in series to provide a
greater voltage.

Question 4

*Chemical cells

Answer 4

Cells contain chemicals which react to produce electricity

Question 5

Endothermic reaction

Answer 5

An endothermic reaction is one that takes in energy from the
surroundings so the temperature of the surroundings decreases. In an endothermic
reaction, the energy needed to break existing bonds is greater than the energy
released from forming new bond

Question 6

Exothermic reaction:

Answer 6

An exothermic reaction is one that transfers energy to the
surroundings so the temperature of the surroundings increases. In an exothermic reaction,
the energy released from forming new bonds is greater than the energy needed to
break existing bonds.

Question 7

*Fuel cells:

Answer 7

Fuel cells are supplied by an external source of fuel (eg hydrogen) and oxygen
or air. The fuel is oxidised electrochemically within the fuel cell to produce a potential
difference

Question 8

Overall energy change of the reaction

Answer 8

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

Question 9

Reaction profile:

Answer 9

: Reaction profiles can be used to show the relative energies of reactants
and products, the activation energy and the overall energy change of a reaction.

Question 10

*Rechargeable cells

Answer 10

: Rechargeable cells and batteries can be recharged because the
chemical reactions are reversed when an external electrical current is supplied.

Question 11

what is activation energy?

Answer 11

minimum amount of energy that particles need to react

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 takes place

Question 13

what is an exothermic reaction?give ecamples

Answer 13

a reaction where energy is transferred to the surroundings so that the surroundings temperature increases - combustion , oxidation reactions and neutralisation. Negative sign of energy change

Question 14

what is an endothermic reaction? Give examples

Answer 14

a reaction where energy is taken in from the surroundings so the surroundings temperature decreases - thermal decomposition , reaction of citric acid and sodium hydrogen carbonate .Negative sign of energy change.

Question 15

what is a reaction profile?

Answer 15

reaction profile is a graph which shows the relative energies of reactants and product , as well as activation energy of the reaction

Question 16

what is a cell?

Answer 16

a cell is composed of two electrodes dipped in an electrolyte solution .It produces electricity from a chemical reaction

Question 17

what is a battery ?

Answer 17

a battery consists of two or more cells connected in series

Question 18

what determines the voltage obtained from a cell?

Answer 18

identities of metal 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

1) more or less cheap , some are rechargeable , convenient source of electrical energy
2) harmful chemicals

Question 20

describe rechargeable and non - rechargeable cells

Answer 20

rechargeable - chemical reactions are reversed when an external current is supplied
non - rechargeable - reactants are used up , cannot be recharged