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CHEMISTRY GCSE > ENERGY CHANGES > Flashcards

ENERGY CHANGES Flashcards

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1
Q

In an exothermic reaction heat and energy is…..

A

given out

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2
Q

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

A

surroundings this is shown by the increase in temperature

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3
Q

examples of exothermic reaction

A

combustion
neutralisation
oxidation
hand warmers(example of oxidation)

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4
Q

in an endothermic reaction heat and energy is….

A

taken in

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5
Q

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

A

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

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6
Q

examples of endothermic reactions

A

sports injury pack

thermal decomposition

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7
Q

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

A

products are lower than the reactants

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8
Q

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

A

the reactants are lower than the products

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9
Q

what is activation energy

A

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

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10
Q

the greater the activation energy….

A

the more energy needed to start the reaction

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11
Q

what does the difference in height show in an energy profile

A

energy change during the reaction

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12
Q

during a chemical reaction….

A

old bonds are broken and new bonds are formed

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13
Q

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

A

endothermic

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14
Q

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

A

exothermic

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15
Q

bond breaking=

A

endothermic

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16
Q

bond making=

A

exothermic

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17
Q

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

A

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

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18
Q

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

A

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

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19
Q

BOND ENERGIES

NEGATIVE=

A

exothermic

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20
Q

BOND ENERGIES

POSITIVE=

A

endothermic

21
Q

how to work out bond energies

A
  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
22
Q

how do catalysts increase the rate of reaction

A

decrease the amount of activation energy needed

23
Q

what is a cell

A

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

24
Q

what material are the electrodes

A

metal as they need to conduct electricity

25
Q

what is an electrolyte

A

is a liquid that contains ions which react with the electrodes

26
Q

chemical reactions in a cell produce…..

A

electricity

27
Q

different materials will react ……. with the same electrolyte

A

differently

28
Q

what effects the voltage of a cell

A

the difference In reactivities between the electrodes

the electrolyte

29
Q

the bigger the difference in reactivity of the electrodes

A

the higher the voltage

30
Q

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

A

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

31
Q

NON rechargeable batteries

A

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

32
Q

example of non rechargeable batteries

A

Alkaline batteries- contains cells which use irreversible reactions

33
Q

in a rechargeable cell

A

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.

34
Q

what do fuel cells use to produce electrical energy

A

fuel and oxygen

35
Q

what is a fuel cell

A

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

36
Q

what happens when the fuel enters the cell

A

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

37
Q

one type of fuel cell

A

hydrogen oxygen fuel cell

38
Q

what type of reaction does a hydrogen oxygen fuel cell involve

A

redox reaction

39
Q

experiment hydrogen fuel cells

A
  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
40
Q

advantages for using hydrogen oxygen fuel cells in cars

A

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

41
Q

disadvantages for using hydrogen fuel cells in cars

A

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

42
Q

half equation at the anode for hydrogen oxygen fuel cells

A

H2— 2H+ (+) 2e-

43
Q

half equation at the cathode for hydrogen oxygen fuel cells

A

O2 + 4H+ (+) 4e- ——- 2H2O

44
Q

in fuel cells the anode is ……

A

negative

45
Q

in fuel cells the cathode is……

A

positive

46
Q

What type of energy is released by hydrogen fuel cells

A

Electrical energy

47
Q

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

A

T

48
Q

why can alkaline batteries not be recharged

A

the reaction is not reversible

49
Q

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

A

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

CHEMISTRY GCSE (13 decks)

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