ENERGY CHANGES

Question 1

In an exothermic reaction heat and energy is…..

Answer 1

given out

Question 2

an exothermic transfers energy to its ,, how is this shown

Answer 2

surroundings this is shown by the increase in temperature

Question 3

examples of exothermic reaction

Answer 3

combustion
neutralisation
oxidation
hand warmers(example of oxidation)

Question 4

in an endothermic reaction heat and energy is….

Answer 4

taken in

Question 5

an endothermic reaction takes in energy from….. and this is shown…

Answer 5

takes energy in from its surroundings and this is shown by a fall in temperature

Question 6

examples of endothermic reactions

Answer 6

sports injury pack

thermal decomposition

Question 7

in an exothermic energy profile where are the reactants and the products

Answer 7

products are lower than the reactants

Question 8

in an endothermic energy profile where are the reactants and the products

Answer 8

the reactants are lower than the products

Question 9

what is activation energy

Answer 9

activation energy is the minimum amount of energy the reactants need to collide with each other and react and to break the bonds

Question 10

the greater the activation energy….

Answer 10

the more energy needed to start the reaction

Question 11

what does the difference in height show in an energy profile

Answer 11

energy change during the reaction

Question 12

during a chemical reaction….

Answer 12

old bonds are broken and new bonds are formed

Question 13

energy must be supplied to break existing bonds so bond breaking is…

Answer 13

endothermic

Question 14

energy is released when new bonds are formed so bond forming is….

Answer 14

exothermic

Question 15

bond breaking=

Answer 15

endothermic

Question 16

bond making=

Answer 16

exothermic

Question 17

in exothermic reactions the energy _______ is ______ than the energy used to break them

Answer 17

in exothermic reactions the energy released is greater than the energy used to break them

Question 18

in an endothermic reaction the energy _____ to break the bonds is________ than the energy released by forming them

Answer 18

in an endothermic reaction the energy used to break the bonds is greater than the energy released by forming them

Question 19

BOND ENERGIES

NEGATIVE=

Answer 19

exothermic

Question 20

BOND ENERGIES

POSITIVE=

Answer 20

endothermic

Question 21

how to work out bond energies

Answer 21

1. write out equation and balance it
2. draw out everything you have
3. work out the bond energies
4. reactants minus products
5. see if it is endo or exothermic

Question 22

how do catalysts increase the rate of reaction

Answer 22

decrease the amount of activation energy needed

Question 23

what is a cell

Answer 23

a cell is a basic system made up out of two different electrodes in contact with an electrolyte

Question 24

what material are the electrodes

Answer 24

metal as they need to conduct electricity

Question 25

what is an electrolyte

Answer 25

is a liquid that contains ions which react with the electrodes

Question 26

chemical reactions in a cell produce.....

Answer 26

electricity

Question 27

different materials will react ……. with the same electrolyte

Answer 27

differently

Question 28

what effects the voltage of a cell

Answer 28

the difference In reactivities between the electrodes | the electrolyte

Question 29

the bigger the difference in reactivity of the electrodes

Answer 29

the higher the voltage

Question 30

how can the electrolyte used in a cell affect the size of voltage

Answer 30

the different ions in solution will react differently with the metal electrodes used

Question 31

NON rechargeable batteries

Answer 31

over time the reacting particles, (the ions in the electrolyte and the metal ions in the electrode) gets used up. once the reactants are used up the reaction cannot happen and so no electricity is produced the products cant be turned back into reactants so the cell cannot be recharged

Question 32

example of non rechargeable batteries

Answer 32

Alkaline batteries- contains cells which use irreversible reactions

Question 33

in a rechargeable cell

Answer 33

the reaction is reversible so once all the reactants have been used up when you connect it to a external electric current electricity will pass through reversing the reaction, recharging the reactants.

Question 34

what do fuel cells use to produce electrical energy

Answer 34

fuel and oxygen

Question 35

what is a fuel cell

Answer 35

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

Question 36

what happens when the fuel enters the cell

Answer 36

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

Question 37

one type of fuel cell

Answer 37

hydrogen oxygen fuel cell

Question 38

what type of reaction does a hydrogen oxygen fuel cell involve

Answer 38

redox reaction

Question 39

experiment hydrogen fuel cells

Answer 39

1. the electrolyte is often a solution of potassium hydroxide, the electrodes are often porous carbon with a catalyst 2. Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment 3. at the anode hydrogen loses electrons to produce h+ ions (THIS IS OXIDATION) 4. H+ ions in the electrolyte move to the cathode 5. at the cathode oxygen gains electrons from the cathode and reacts with H+ ions from the electrolyte to make water (THIS IS REDUCTION) 6. the electrons flow through an external circuit from the anode to the cathode - that is the electric current

Question 40

advantages for using hydrogen oxygen fuel cells in cars

Answer 40

fuel cell vehicles don't produce as many pollutants as other fuels as their only by products are water and heat batteries are more expensive to make than fuel cells theres a limit on how many times the batteries can be recharged before they need replacing fuel cells store more energy than batteries do batteries are more polluting to dispose of as they are made of highly toxic metal compounds

Question 41

disadvantages for using hydrogen fuel cells in cars

Answer 41

hydrogen is a gas so it takes up loads more space to store than a rechargeable battery hydrogen is explosive when mixed with air so its hard to store safely

Question 42

half equation at the anode for hydrogen oxygen fuel cells

Answer 42

H2--- 2H+ (+) 2e-

Question 43

half equation at the cathode for hydrogen oxygen fuel cells

Answer 43

O2 + 4H+ (+) 4e- ------- 2H2O

Question 44

in fuel cells the anode is …...

Answer 44

negative

Question 45

in fuel cells the cathode is......

Answer 45

positive

Question 46

What type of energy is released by hydrogen fuel cells

Answer 46

Electrical energy

Question 47

Describe what must happen to the molecules of X and Y to allow them to react.

Answer 47

T

Question 48

why can alkaline batteries not be recharged

Answer 48

the reaction is not reversible

Question 49

a student used test tubes when he investigated the volume of gases produced during electrolysis its wrong what should be changed

Answer 49

use measuring cylinders instead of test tubes because test tubes cannot measure volume