energy changes 5

Question 1

what happens to energy in a reaction

Answer 1

energy is conserved in reactions and only move around

Question 2

what is an exothermic reaction

Answer 2

one that transfers energy to the surroundings usually by heating

Question 3

examples of exothermic reactions

Answer 3

combustion
neutralisation reactions
oxidation reactions

Question 4

what is an endothermic reaction

Answer 4

one that takes in energy from the surroundings

Question 5

examples of endothermic reactions

Answer 5

thermal decomposition

reaction between citric acid and sodium hydrogencarbonate

Question 6

everyday uses of endothermic reactions

Answer 6

sports injury packs (allow the pack to become instantly cooler)

Question 7

everyday uses of exothermic reactions

Answer 7

hand warmers(oxidation of iron in air to release energy)
self heating cans(chemicals in there base)

Question 8

what happens to bonds during a reaction

Answer 8

old bonds break and new ones form

Question 9

what reaction is bond breaking

Answer 9

endothermic

Question 10

what reaction is bond forming

Answer 10

exothermic

Question 11

what reaction has a minus in bond calculations

Answer 11

exothermic

Question 12

what reaction has plus in bond calculations

Answer 12

endothermic

Question 13

what are reaction profiles

Answer 13

diagrams that show the relative energies of the reactants and products in a reaction

Question 14

what is the activation energy

Answer 14

the initial rise. and is the minimum amount of energy the reactants need to collide with each other and react.

Question 15

what does the difference in height mean in reaction profiles

Answer 15

represents the overall energy change in the reaction

Question 16

what is at higher energy by the end of an exothermic reaction. Product or reactant

Answer 16

reactants

Question 17

what is at higher energy by the end of an endothermic reaction. Product or reactant

Answer 17

products

Question 18

what is an eletrochemical cell

Answer 18

a basic system made up of two different electrodes in contact with an electrolyte
two electrodes are usually metal

Question 19

what is electrolyte

Answer 19

a liquid that contains ions that react with the electrodes

Question 20

how cells produce energy

Answer 20

chemical reaction between the electrodes and the electrolyte set up a charge difference between the electrodes.
If the electrodes are then connected by a wire, the charge is able to flow and produces electricity.

Question 21

what factors change the voltage of a cell

Answer 21

type of electrodes

electrolyte

Question 22

what happens in a normal cell

Answer 22

chemical reaction at the electrode are irreversible

the ions in the electrlyte and the metal ions on the electrode get used up

Question 23

what happens in a re chargeable cell

Answer 23

reaction can be reversed by connecting it to an external electric current

Question 24

how is a battery formed

Answer 24

connecting two or more cells together in series

Question 25

disadvantages of using hydrogen fuel cells

Answer 25

Takes up lots of space
explosive so hard to store
hydrogen made from hydrocarbons which mean they still pollute

Question 26

advantages of using hydrogen fuel cells

Answer 26

don’t produce as many pollutants
batteries are more expensive
batteries store less energy so need charging
batteries need replacing

Question 27

why batteries are better than conventional fuels

Answer 27

conventional fuels have finite supply

batteries and fuel cells are cleaner

Question 28

what is a fuel cell

Answer 28

is an electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy sufficiently

Question 29

how do fuel cell work

Answer 29

fuel enters the cell it becomes oxidised and sets up a potential difference within the cell

Question 30

how hydrogen oxygen fuel cell works

Answer 30

Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment

at the anode hydrogen loses electrons to produce H plus ions

H plus ions in the electrolyte move to the cathode

at the cathode oxygen gains electrons from the cathode and reacts with H plus ions to make water

the electrons flow through an external circuit from anode to cathode

overall reaction is hydrogen + oxygen = water