energy changes

Question 1

each reactant all has

Answer 1

differents amount of chemical energy in their chemical energy store

Question 2

what is on the y and x axis for a reaction profile diagram

Answer 2

the y axis is the energy
the x axis is the progress of the reaction

Question 3

when the products have less energy than the reactants where is everything placed on the reaction profile and what type of reaction would it be

Answer 3

exothermic
1)reactants at the top left starting the graph but not touching y axis

2)products much lower down as they have lost a lot of energy but the start aligning with the end of the reactants

3)straight arrow line drawn down saying energy released

Question 4

what is an example of exothermic reactions

Answer 4

combustion reaction
oxidation
neutralisation(base and acid)

Question 5

what are examples of exothermic reactions

Question 6

what would the reaction profile for an endothermic reaction look like

Answer 6

reactants would be low at the bottom left
products would be high starting at the end of reactants
there would be an up facing arrow drawn for energy absorbed

Question 7

what is activation energy

Answer 7

the minimum amount of energy needed for the reactant particles to collide and react

Question 8

how does the activation energy link to starting the reaction

Answer 8

the higher the activation the more energy required to start the reaction

Question 9

how can we show the activation energy in the reaction profiles

Answer 9

by drawing a curve from products to reactants

the increase in energy from the reactants level to the highest point in our curve is called the activation energy

Question 10

what is bond energy

Answer 10

the amount of energy needed to break one mole (6x10(23)of a particular covalent bond

Question 11

is bond breaking endothermic or exothermic and why

Answer 11

it is endothermic as it requires energy from the surroundings

Question 12

bond making is

Answer 12

exothermic-releases energy to surroundings

Question 13

what is the equation for energy change

Answer 13

energy required to break bonds- energy released by forming bonds

or
energy of reactants - energy of products

Question 14

what does a - energy change mean

Answer 14

the reaction is exothermic
as chemicals lose that value to surroundings

Question 15

what 3 things happen in a chemical reaction

Answer 15

The bonds of the reactant molecules are broken
The atoms rearrange themselves
The bonds of the product molecules are formed

Question 16

what are electrochemical cells

Answer 16

cell made by connecting 2 different electrodes and placing them in contact with an electrolyte all connected to a voltmeter

Question 17

how do batteries compare electrochemical cells

Answer 17

they are 2 or more cells connected in series for a greater voltage

Question 18

what 3 factors affect the voltage of a cell

Answer 18

-The metals used for the two electrodes. The greater the difference in reactivity of the two metals, the greater the voltage will be.

-The type and concentration of the electrolyte used.

-The conditions, such as temperature.

Question 19

why are rechargable cells/batteries rechargable

Answer 19

Rechargeable cells and batteries can be recharged because the chemical reactions are reversed when an external electrical current is supplied. These are the batteries used in laptops and mobile phones.

Question 20

why are non rechargable cells not rechargable

Answer 20

chemical reaction stop when 1 reactant has been used up
eg:batteries used in smoke alarms or tv remotes
alkaline batteries are an example

Question 21

why do electrochemical cells have their names

Answer 21

converts chemical energy to electrical

a fuel and oxygen into electrical energy which we can use as power

Question 22

what do hydrogen fuel cells do

Answer 22

combine hydrogen and oxygen to form water while generating a lot of electrical energy

Question 23

what is the structure of hydrogen oxygen cell

Answer 23

electrolyte(commonly potassium hydroxide) in between electrodes with anode (negative)on left and cathode(negative) at top connected by wire at the top

the electrodes are the opposite of electrolysis

Question 24

what do fuel cells have/features

Answer 24

electrodes are made of porous carbon with catalyst

they have anode compartment outside electrode with an inlet at the top where hydrogen enters

cathode compartment inlet where oxygen enters

Question 25

when the fuel cell reaction finishes what happens

Answer 25

the heat and water leave through the cathode compartment outlet

Question 26

how do fuel cells work

Answer 26

hydrogen enters and is oxidised by anode and becomes a hydrogen ion

this equation is
h2—–> 2h+ +2e-

then the electrons flow around wire to the cathode

the hydrogen ions pass the electrode to the cathode

they react with the oxygen that comes in from the cathode inlet combining to make water

Question 27

what is the fuel cell equation at the cathode

Answer 27

o2+ 4h+ +4e- ——-> 2h2o

Question 28

when the electrons in a half equation are on the right /left

Answer 28

right is loss
left is gain

Question 29

what is the overall equation

Answer 29

o2+ 2h2 —>2h2o

Question 30

where does this electrical energy come from in a fuel cell

Answer 30

from the movement of electrons through the wire and is powered by the chemical reaction

Question 31

how do fuel cells work

Answer 31

as fuel enters cell it gets oxidised setting up pd across cell

Question 32

pros and cons of fuel cells

Answer 32

pros
-replace polluting fossil fuel engines and batteries we have in vehicles
-only need hydrogen and oxygen
-no waste pollutants
-simple devices
-last longer than batteries
-less polluting to dispose of

cons
-hydrogen takes up much more space than fossil fuels
-explosive in air
-requires energy to make which often comes from fossil fuels