chemistry topic 5 energy changes

Question 1

whats an exothermic reaction ?

Answer 1

a reaction which transfers energy to the surroundings usually by heating. this is shown by a rise in temperature

Question 2

what reactions are exothermic?

Answer 2

combustion, neutralisation and oxidisation

Question 3

what everyday objects provide exothermic reaction?

Answer 3

hand warmers and self heating cans

Question 4

what is an endothermic reaction?

Answer 4

one which takes in energy from the surrounding. this is shown by a fall in temperature

Question 5

whats an example of an endothermic reaction?

Answer 5

thermal decomposition

Question 6

what everyday objects provide an endothermic reaction?

Answer 6

sports injury packs

Question 7

how can you measure energy transfer in a practical?

Answer 7

taking the temperature of reagents, putting them in a polystyrene cup, mixing them and then measuring the temperature at the end

Question 8

what is the biggest problem when measuring energy transfer?

Answer 8

energy can be lost in the surroundings

Question 9

how can you reduce energy loss when measuring energy transfer?

Answer 9

put a lid on the cup and put more insulation in the cup e.g. cotton wool

Question 10

what is bond breaking ? exothermic or endothermic?

Answer 10

endothermic

Question 11

why is bond breaking an endothermic reaction?

Answer 11

energy must be supplied to break existing bonds

Question 12

what is bonds formed? endothermic or exothermic?

Answer 12

exothermic

Question 13

why is bond formation an exothermic reaction?

Answer 13

energy is released when new bonds are formed

Question 14

in exothermic reactions the energy released by forming bonds is ?

Answer 14

greater than the energy used to break them

Question 15

in endothermic reactions the energy used to break the bonds is?

Answer 15

greater than the energy released by forming them

Question 16

in an exothermic reaction profile where are the products compared to the reactants?

Answer 16

the products are at a lower energy than the reactants

Question 17

in an exothermic reaction profile what does the difference between products and reactants mean?

Answer 17

the overall energy change in the reaction

Question 18

in an exothermic reaction profile what does the first rise in the line represent?

Answer 18

the energy needed to break the old bonds and start the reaction

Question 19

in an exothermic and endothermic reaction profile what is the first initial rise called?

Answer 19

the activation energy

Question 20

in an exothermic and endothermic reaction profile what is the activation energy?

Answer 20

the minimum amount of energy the reactants need to collide with each other and react

Question 21

in an endothermic reaction profile where are the products compared to the reactants?

Answer 21

the products are at a higher energy than the reactants

Question 22

in an endothermic reaction profile, what does the overall energy change mean?

Answer 22

the overall energy taken in

Question 23

what is the equation for overall energy change?

Answer 23

overall energy change= energy required to break bonds-energy released by forming bonds

Question 24

when finding bond energies what do you do?

Answer 24

add up the energies of your products and reactants then take them away reactants - products

Question 25

what is an electrcochemical cell?

Answer 25

a basic system made up of two electrodes in contact with an electrolyte

Question 26

exothermic endothermic practical: what do you prepare in separate beakers?

Answer 26

25 cm cubed of hydrochloric acid (o.25 mol/dm3) and sodium hydroxide

Question 27

exothermic endothermic practical: what do you do with your beakers at the start?

Answer 27

place the beakers in a water bath set to 25 degrees until they are the same temperature

Question 28

exothermic endothermic practical: what do you do after the beakers are the same temperature?

Answer 28

add the HCl followed by the NAOH to a polystyrene cup with a lid

Question 29

exothermic endothermic practical: how often do you take the temperature and what do you record?

Answer 29

every 30 seconds and record highest temperature

Question 30

exothermic endothermic practical: what do you repeat the practical using?

Answer 30

0.5 mol/dm3 and 1 mol/dm3 of hydrochloric acid

Question 31

what must the two electrodes be able to do in an electrochemical cell?

Answer 31

conduct electricity

Question 32

what is the electrolyte in a electrochemical cell?

Answer 32

a liquid that contains ions which react with other electrodes

Question 33

what do the chemical reactions between the electrodes and the electrolyte set up in an electrochemical cell?

Answer 33

charge differences between the electrode

Question 34

if the electrochemical cell has electrodes connected by wire, what can charge do?

Answer 34

flow and electricity Is produced

Question 35

what can be connected to an electrochemical cell to measure volts?

Answer 35

voltmeter

Question 36

the bigger the difference in reactivity of the electrodes, the bigger the what?

Answer 36

voltage of the cell

Question 37

how will the electrolyte used affect the voltage?

Answer 37

different ions will react differently with the electrodes used

Question 38

how is a battery formed?

Answer 38

by connecting two or more cells together in series

Question 39

what kind of reaction happens in a non rechargeable battery?

Answer 39

irreversible one

Question 40

what happens over time to reacting particles in a non rechargeable cell?

Answer 40

the ions in the electrolyte and electrode get used up and turn into products for the reaction

Question 41

once the reactants are all used up in non rechargeable batteries what happens?

Answer 41

reaction cant happen and no electricity is produced as reaction cant be reversed

Question 42

how do rechargeable batteries work again?

Answer 42

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

Question 43

what is the chemical name for a non rechargeable battery?

Answer 43

alkaline battery

Question 44

what is a fuel cell?

Answer 44

an electrical cell supplied with fuel and oxygen- it uses energy from the reaction between them to produce electrical energy efficiently

Question 45

when fuel enters a fuel cell what happens?

Answer 45

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

Question 46

whats an example of a fuel cell?

Answer 46

hydrogen- oxygen fuel cell

Question 47

what happens in a hydrogen oxygen fuel cell?

Answer 47

it combines hydrogen and oxygen to produce nice clean water and energy

Question 48

how are hydrogen-oxygen fuel cells used in vehicles?

Answer 48

conventional fuels like petrol are finite and very polluting therefore vehicles use electrical energy to power them

Question 49

advantages of hydrogen-oxygen fuel cells: what don't they produce?

Answer 49

many pollutants (carbon monoxide carbon dioxide etc)

Question 50

advantages of hydrogen-oxygen fuel cells: what are the only by-products of them?

Answer 50

water and heat

Question 51

advantages of hydrogen-oxygen fuel cells: electric vehicles car cells don't produce many pollutants however what is it like to dispose of them ?

Answer 51

more polluting because they're made from highly toxic metal compounds

Question 52

hydrogen-oxygen fuel cells: what is bad about the rechargeable electric batteries in cars?

Answer 52

theres a limit on how many times you can recharge them before they need replacing

Question 53

of hydrogen-oxygen fuel cells: what is the cost like of a rechargeable cell?

Answer 53

they are more expensive than fuel cells

Question 54

hydrogen-oxygen fuel cells: what don't batteries store as much compared to fuel cells?

Answer 54

less energy- they need to be recharged more often

Question 55

in a hydrogen-oxygen fuel cell what is the electrolyte often?

Answer 55

potassium hydroxide

Question 56

where does hydrogen and oxygen go in a fuel cell?

Answer 56

hydrogen goes in the anode compartment and oxygen goes in the cathode comnpartment

Question 57

what happens at thenegative electrode in a fuel cell?

Answer 57

hydrogen loses electrons to produce H+ ions. this is oxidation

Question 58

where do the H+ ions move in a fuel cell?

Answer 58

they move to the cathode

Question 59

what happens at the positive electrode in a fuel cell?

Answer 59

oxygen gains electrons from the cathode and react with h+ ions to make water. this is reduction

Question 60

where do electrons flow in a fuel cell?

Answer 60

through an external circuit from the anode to cathpde (the electric current)

Question 61

what is the overall reaction for a hydrogen- oxygen fuel cell?

Answer 61

hydrogen + oxygen = water

Question 62

how is a fuel cell a redox reaction?

Answer 62

theres reduction at cathode and oxidation at anode

Question 63

when something is oxidised where are the electrons in the half equation?

Answer 63

last thing

Question 64

when something is reduced where are the electrons in the half equation?

Answer 64

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