Energy Changes

Question 1

what is an exothermic reaction

Answer 1

transfers energy to the surroundings e.g. combustion and neutralization reactions

Question 2

what is an example of a use of an exothermic reaction

Answer 2

hand warmers

self heating cans

Question 3

what is an endothermic reaction

Answer 3

takes in energy from the surroundings e.g. thermal decomposition

Question 4

what is a use of endothermic reactions

Answer 4

a cold pack

Question 5

how is the overall energy change shown on a reaction profile

Answer 5

difference between the energy of the reactants and energy of the products

Question 6

what does an endothermic reaction profile look like

Answer 6

the product is higher than the reactant

Question 7

why does the line go up to begin with on a reaction profile

Answer 7

this is the activation energy. energy required to break the bonds of the reactants.

Question 8

what is activation energy

Answer 8

the minimum energy needed for the reactants to react when they collide

Question 9

how many joules are there in a kilojoule

Answer 9

1000

Question 10

what is the unit of energy transfer usually measured in

Answer 10

kJ/mol

Question 11

is breaking bonds endothermic or exothermic

Answer 11

endothermic cus energy must be supplied to break the bonds

Question 12

is bond forming exothermic or endothermic

Answer 12

exothermic because energy is released

Question 13

if the energy required for bond breaking is more than the energy is released in bond making, will the reaction be exothermic or endothermic

Answer 13

endothermic

Question 14

energy change = energy of bond breaking - ?

Answer 14

energy of bond making

Question 15

what is a cell

Answer 15

a system that contains chemicals which react and produce electricity

Question 16

how do cells work

Answer 16

it has two different electrodes and an electrolyte which is a liquid that can conduct electricity and contains ions that react with the electrodes

the reactions between the electrodes and electrolyte set up a charge difference between the electrodes . if the electrodes are connected by a wire the charge is able to flow and electricity is produced

Question 17

how can you maximize the voltage of a cell

Answer 17

the bigger the difference in reactivity of the electrodes, the bigger the voltage

the concentration of ions in the electrolyte also impacts on the voltage

Question 18

how is a battery formed

Answer 18

connecting two or more cells together in series

Question 19

the voltage of a battery is what of the cells that it is made of

Answer 19

equal to the voltages of all the cells added together

Question 20

are alkaline batteries rechargeable

Answer 20

no

Question 21

what is a fuel cell

Answer 21

a cell that works on a fuel and oxygen. it efficiently transfers energy as electricity

Question 22

how does a fuel cell work

Answer 22

fuel enters the cell at one side where it becomes oxidised and sets up a potential difference which powers the device. the air enters the cell at the other side where it reacts to form water

Question 23

what is the electrolyte of a a hydrogen oxygen fuel cell

Answer 23

a solution of potassium hydroxide

Question 24

in hydrogen fuel cells, what goes to the cathode (positive) and what goes to the anode (negative)

Answer 24

hydrogen goes to the anode

oxygen goes to the cathode

Question 25

what happens at the anode (negative electrode) in a hydrogen fuel cell

Answer 25

oxidation.

hydrogen loses electrons to produce H+ ions and then the H+ ions move to the cathode

Question 26

what happens at the cathode (positive electrode) in hydrogen fuel cells

Answer 26

reduction.

oxygen gains electrons, then reacts w H+ ions to make water

Question 27

in a hydrogen fuel cell the electrons flow from the anode to the cathode through an external circuit

Answer 27

the overall reaction is redox reaction

2H2 + O2 = 2H2O

Question 28

what is the half equation for the reaction at the anode of a hydrogen fuel cell

Answer 28

h2 = 2H + 2e-

Question 29

what is the half equation for the cathode in a hydrogen fuel cell

Answer 29

o2 + 4H+ + 4e- = 2H2O

Question 30

advantages of hydrogen fuel cells

Answer 30

don’t produce as many pollutants as other fuels- even electric cars cus there batteries are polluting to dispose of

fuel cells are cheaper than batteries and last longer

batteries need to be recharged more often

Question 31

disadvantages of hydrogen fuel cells

Answer 31

hydrogen takes up more space to store

hydrogen is explosive when mixed with air so hard to store safely

hydrogen fuel is often made from hydrocarbons or by electrolysis of water which uses electricity