C5/Energy Changes

Question 1

what happens to energy in chemical reactions?

Answer 1

energy is conserved

Question 2

the amount of energy in the universe at the end of a chemical reaction is the same as what?

Answer 2

it is the same as before the reaction takes place

Question 3

an exothermic reaction is one of that transfers energy where?

Answer 3

to the surroundings, so the temperature of the surroundings increases (a heat is given out)

Question 4

give examples of exothermic reactions

Answer 4

combustion
many oxidation reactions
neutralisation

Question 5

give some everyday uses of exothermic reactions

Answer 5

self-heating cans

hand warmers

Question 6

an endothermic reaction is one that transfers energy where?

Answer 6

it takes energy from the surroundings, so the temperature of the surroundings decreases (as heat is taken in)

Question 7

give examples of an endothermic reaction

Answer 7

thermal decompositions

reaction of citric acid and sodium hydrogencarbonate

Question 8

give an everyday use of an endothermic reaction

Answer 8

sports injury packs

Question 9

chemical reactions can occur only when reacting particles collide with each other and with sufficient what?

Answer 9

energy

Question 10

the minimum amount of energy that particles must have to react is called with?

Answer 10

the activation energy

Question 11

what type of diagram can be used to show the relative energies of reactants and products, the activation energy and the overall energy change of a reaction?

Answer 11

reaction profile diagram

Question 12

during a chemical reaction energy must be supplied to break the bonds in what?

Answer 12

in the reactants

Question 13

during a chemical reaction energy is released when bonds in the products are what?

Answer 13

when bonds are formed

Question 14

what can be calculated from the energy needed to break bonds minus the energy released when bonds are formed?

Answer 14

the bond energies

Question 15

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 is called what?

Answer 15

the overall energy change of the reaction

Question 16

in what type of reaction is the energy released from forming new bonds greater than the energy needed to break existing bonds?

Answer 16

in an exothermic reaction

Question 17

in what type of reaction is the energy needed to break existing bonds is greater than the energy released from forming new bonds?

Answer 17

in an endothermic reaction

Question 18

cells contain chemicals which react to produce what?

Answer 18

electricity

Question 19

the voltage produced by a cell is developed upon a number of factors.
name 2 of these.

Answer 19

the type of electrode

the type of electrolyte

Question 20

describe how a simple cell can be made (battery)

Answer 20

by connecting two different metals in contact with an electrolyte

Question 21

batteries consist of what?

Answer 21

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

Question 22

in non-rechargeable batteries and cells the chemical reactions stop when what happens?

Answer 22

one of the reactants has been used up

Question 23

name a non-rechargeable type of battery

Answer 23

alkaline batteries

Question 24

rechargeable batteries and cells can be recharged because the chemical reactions are reversed when what is supplied?

Answer 24

when an external electrical current is supplied

Question 25

fuel cells are supplied by an external source of fuel and what?

Answer 25

oxygen or air

Question 26

what happens to the fuel within the fuel cell when it produces a potential difference?

Answer 26

it is oxidised electrochemically

Question 27

the overall reaction in a hydrogen fuel cell involves the oxidation of hydrogen to produce what?

Answer 27

water

Question 28

hydrogen fuel cells offer a potential alternative to what?

Answer 28

rechargeable cells and batteries