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Chemistry GCSE > topic 7 - rates of reaction and energy changes > Flashcards

topic 7 - rates of reaction and energy changes Flashcards

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1
Q

rate of reaction formula

A

time

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2
Q

what are three ways of measuring reaction rate

A

change in mass
volume of gas given off
precipitation

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3
Q

describe how rate of reaction is measured in terms of change in mass (when a gas is produced)

A

using a mass balance
as the gas is released, the lost mass is easily measured on the balance (the quicker the reading is dropping, the higher the reaction rate)
plot graph of change in mass against time elapsed

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4
Q

what should you do if the gas being released is dangerous

A

use a fume cupboard

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5
Q

describe how rate of reaction is measured in terms of volume of gas given off

A

using a gas syringe
the more gas given off in set time interval, the faster the reaction
once no more gas is produced, the reaction is finished
plot results on graph of gas volume against time elapsed

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6
Q

describe how rate of reaction is measured in terms of a precipitation

A

two reactant solutions are mixed in a flask which is placed on a piece of paper with a mark on it
observe the mark through the mixture and time how long it takes for it to be obscured (the faster the mark disappears, the faster the reaction)

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7
Q

why is measuring rate of reaction in terms of a precipitation subjective

A

people may have different opinions on when the mark disappears

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8
Q

what three factors affect reaction rate

A

surface area
concentration/pressure
temperature

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9
Q

the steeper the slope on a rate of reaction graph…

A

the faster the rate of reaction

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10
Q

to find the gradient on a curve

A

draw a tangent and calculate the gradient of that straight line
that gradient is the rate at that point

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11
Q

investigating the effect of surface area on rate of reaction: uses what reactants

A

hydrochloric acid

marble chips

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12
Q

investigating the effect of surface area on rate of reaction: describe the method

A

measure volume of gas with a gas syringe (taking readings at regular intervals and recording them in a table)
plot results on a graph (volume against time)
repeat with the same VOLUME and CONCENTRATION of acid and same MASS of chips but with the chips MORE crushed up, to increase surface area
REPEAT

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13
Q

investigating the effect of surface area on rate of reaction: results

A

the finer the particles, the greater the rate of reaction

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14
Q

investigating the effect of concentration on rate of reaction: uses what reactants

A

hydrochloric acid

marble chips

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15
Q

investigating the effect of concentration on rate of reaction: describe the method (2 possible)

A

OR
–
measure the change in mass during the reaction
place a flask with a set concentration of HCl on a mass balance
add marble chips and immediately note the mass shown on the balance
record the mass at regular intervals
plot mass lost against time on a graph
repeat with different concentrations of acid

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16
Q

investigating the effect of temperature on rate of reaction: reactants and reaction

A

observed colour change from precipitation reaction between sodium thiosulfate and hydrochloric acid

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17
Q

investigating the effect of temperature on rate of reaction: describe the method (6/7)

A

1) (sodium thiosulfate solution and hydrochloric acid react to form a yellow precipitate of sulfur)
2) measure out fixed volumes of the two solutions using a measuring cylinder
3) gently heat both solutions to the desired temperature using a water bath before mixing them
4) mix solutions in a conical flask and place flask over a black mark
5) time how long it take for the mark to disappear as the precipitate forms
6) repeat at different temperatures
7) plot results on graph of time taken for mark to disappear against temperature of reacting solutions

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18
Q

investigating the effect of temperature on rate of reaction: results

A

increasing temperature, increases rate of reaction

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19
Q

activation energy

A

the minimum energy that particles need in order to react when they collide
AND
the minimum amount of energy for bonds to break

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20
Q

why does increasing temperature, increase rate of reaction

A

when temperature increases, particle have more kinetic energy so move more quickly
when they move more quickly, there are more frequent collisions
therefore at higher temperatures, THERE WILL BE MORE SUCCESSFUL COLLISIONS, increasing rate of reaction

21
Q

why does increasing concentration/pressure, increase rate of reaction

A

if a solution is more concentrated, there are more reactant particles in the same volume/are more crowded so collisions are more likely and the rate of reaction increases

22
Q

why does increasing surface area, increase rate of reaction

A

increasing the surface area of an object gives it a greater surface area to volume ratio
the particles surrounding it have a larger area to work on so the frequency of collisions will increase
this increases rate of reaction

23
Q

catalyst

A

a substance that increases the rate of reaction without being chemically change or being used up in the reaction itself

24
Q

how do catalysts increase rate of reaction

A

catalysts lower the activation energy needed for a reaction to occur by providing an ALTERNATIIVE REACTION PATHWAY (which has a lower activation energy)

therefore, more particles have the minimum amount of energy needed for a reaction when particles collide so more successful collisions occur

25
Q

what are enzymes

A

biological catalysts

26
Q

what do biological catalysts do (examples of reactions they are involved in)

A

speed up chemical reactions within cells such as respiration, photosynthesis and protein synthesis

27
Q

what do enzymes in yeast cells do

A

they are involved in fermentation, which is used to make alcoholic drinks
they catalyse the reaction converting sugars to ethanol and CO2

28
Q

exothermic reaction

A

a reaction which gives out energy to the surroundings, usually in the form of heat and is shown by a rise in the temperature of the surroundings

29
Q

endothermic reaction

A

a reaction that takes in energy from the surroundings, usually in the form of heat and is show by a fall in the temperature of the surroundings

30
Q

describe the curve on the reaction profile of an exothermic reaction

A

curves downwards (ends lower than it started)

31
Q

describe the curve on the reaction profile of an endothermic reaction

A

curves upwards (ends higher than it started)

32
Q

what is the activation energy on a reaction profile

A

the distance between the reactants and the highest point on the curve

33
Q

how to measure temperature change in surroundings

A
  • place a polystyrene cup in a large beaker of cotton wool
  • add known volume of first reagent to cup
  • measure initial temperature
  • add a measured mass/volume of second reagent to cup and stir
  • put lid on cup (to reduce energy loss by evaporation)
  • record maximum or minimum tempature
  • calculate temperature change
34
Q

precipitation reaction

A

when two solutions are mixed together to form an insoluble solid

35
Q

are precipitation reactions endothermic or exothermic

A

exothermic

36
Q

displacement reaction

A

a more reactive element displaces a less reactive element from a compound

37
Q

are displacement reactions endothermic or exothermic

A

exothemic

38
Q

neutralisation reaction

A

acid and base react together to form a salt and water

39
Q

are most neutralisation reactions endothermic or exothermic

A

most neutralisation reactions are exothermic

40
Q

give an example of an endothermic neutralisation reaction

A

ethanoic acid + calcium carbonate

41
Q

dissolving salts in water is exothermic or endothermic

A

can be both

42
Q

bond breaking

A

energy must be supplied to break existing bonds

bond breaking is an ENDOTHERMIC process

43
Q

bond forming

A

energy is released when new bonds are formed

bond formation is an EXOTHERMIC process

44
Q

energy for bonds broken/formed in endothermic reactions

A

more energy is used to break bonds than is released by forming them

45
Q

energy for bonds broken/formed in exothermic reactions

A

more energy is released by forming bonds than by breaking them

46
Q

how to calculate overall energy change

A

energy need to break bonds - energy released by forming bonds

47
Q

what does it mean if the overall energy change is POSITIVE

A

endothermic reaction

48
Q

what does it mean if the overall energy change is NEGATIVE

A

exothermic reaction

Chemistry GCSE (15 decks)

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