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Chemistry > C5 Controlling Chemical Reactions > Flashcards

C5 Controlling Chemical Reactions Flashcards

1
Q

1 what is rate of reaction

A

how fast the reactants are turning into products

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2
Q

1 how do you measure the rate of reaction

A

ROR = amount of product made / time taken
ROR = amount of reactant used / time taken

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3
Q

1 what is a low ROR
what is a high ROR

A

low = slow ROR
high = fast ROR

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4
Q

1 what is collision theory

A

particles must collide with enough energy and in the correct orientation in order to react successfully
any change that increases the chances of particles colliding into one another will increase the rate of reaction

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5
Q

1 what happens when experimenting with magnesium + hydrochloric acid -> ?

A

the lower the temperature the slower the time and therefore the slower the rate of reaction

when the particles have more kinetic energy more successful collisions occur

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6
Q

1 what happens when tempertaure is increased?

A

reactant particles move more quickly and more have an energy higher than the activation energy
the particles collide more often and with more force leading to greater frequency of successful collisions
ROR increases

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7
Q

1 how do you measure ROR in practicals

A

time how long it takes for a solid reactant to disappear
collect gas formed in an inverted measuring cylinder full of water over a water bath
measure the mass lost as a gas is forme and allowed to escape
timing how long it takes for a solution to turn cloudy
collecting gas formed in a gas syringe over time

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8
Q

1 how does a small surface area help?

A

as particle size gets smaller, surface area increases
more particle exposed
collisions more likely
ROR increase

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9
Q

2 what is low concentration

what is high concentration

A

low amount of particles in a fixed area

high amount of particles in a fixed area

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10
Q

2 what happens when concentration of a solution is increased

A

more reactants in a volume
particles are more crowded
particles are more likely to collide so a greater frequency of successful collisions
ROR increases

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11
Q

2 if the pressure of reacting gases is increased

A

volume decreases
particles are more crowded
particles are more likely to collide so a greater frequency of successful collisions
ROR increases

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12
Q

2 what experiment do you do to measure the effect of concentration on reaction rate?

A

a chemical reaction over a piece of paper with a cross on it
time how long until you dont see the cross with different concentrations of solutional mix

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13
Q

2 how does sodium thiosulfate solution with sulphur acid measure ROR

A

different amounts of sulfur acid are added to create the solide sulphur
timing how long the reaction takes (how long until the cross disappears) gives you the data to work out ROR
then you can see if concentration affects ROR or not

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14
Q

2 what was the outcome of the experiement

A

a higher concentration of sulphur acid takes longer time

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15
Q

4 what produces the most gas in 10 seconds?
small or large marble chips

A

small marble chips

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16
Q

4 what is marble

A

calcium carbonate

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17
Q

4 what does higher surface area mean?

A

more collisions
more particles are exposed so more successful collisions occur

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18
Q

4 why do the lines join on a graph showing a HSA to LSA reactions

A

the same amount of reactants are used and therefore same amount of products are made

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19
Q

5 what is a catalytic converter

A

all cars have it in there exhaust
converts pollutants into less harmful gases
carbon monoxide into carbon dioxide
nitrogen dioxide into nitrogen and oxygen
makes acid rain
metals like rhodium and platinum are used in a honey comb structure
maximum surface area

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20
Q

5 what is a catalyst

A

a substance that speeds up the reaction without chemically changing itself
different catalysts are used for different chemical reactions

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21
Q

5 how do you experiment with a catalyst

A

add washing up liquid to see oxygen rising
add catalysts to potato liver and manganese dioxide
add hydrogen peroxide and time till it gets to the top
potato had the smallest reaction
liver was relatively fast- lots of bubbles
MgO2 very fast and bubbly and most successful

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22
Q

5 how do catalysts change?

A

they don’t
they stay completely the same
so they can be used for multiple reactions
some work better than others though

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23
Q

5 what does a catalyst actually do

A

lower the activation energy needed for a successful collision
so more of the reactants have the energy required to start the reaction
more collisions happen to the rate of reaction increases

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24
Q

6 why is food put in the fridge so it keeps for longer

A

when particles are cooler they are stationary and less likely to bump into each other, causing a chemical reaction
hence why food is kept in the fridge so it stays nice for longer

25
Q

6 what does the mean rate of reaction tell you

A

mean ROR after or between a certain period of time

26
Q

6 Mean ROR equation

A

Mean ROR = quantity of product made / time
Mean ROR = quantity of reactant used / time

27
Q

6 how do you calculate the rate at specific time

A

draw a tangent to the point given and work out the gradient of the tangent line

28
Q

6 why is ROR graphs often plotted with 1/time

A

it shows the reaction rate more easily and the trend can be seen better

29
Q

7 what is a physical change

A

no new substance made
usually reversible
ice -> water

30
Q

7 what is a chemical change

A

new substance made/ change in state
usually not reversible
baking a cake
iron rusting
change in pH, sound, temperature, colour, light

31
Q

7 what are reversible reactions

A

many of them
they go to completion- where all the reactants are used up
products formed can react to form the original reactants
the arrow is double headed

32
Q

7 which way is exothermic
which is endothermic

A

exothermic is your normal equation (release energy)
A+B -> C+D

endo thermic is the backwards one (absorb energy)
A+B <- C+D

33
Q

7 whats an open system

A

when reactants or products can escape or be added

34
Q

7 whats a closed system

A

when neither reactants nor products can escape of be added
eventually reach an equilibrium state

35
Q

7 what is ammonium chloride

A

NH4Cl
NH3 - ammonia
HCl - hydrochloric acid
NH3 + HCl -> NH4Cl

REVERSIBLE REACTION
not a sublimation reaction

36
Q

7 what happens to ammonium chloride with litmus paper

A

red litmus paper turns blue
- ammonia present / alkali

blue litmus paper turns red
- hydrogen chloride present / acid

37
Q

7 what is ammonium chloride (S/L/G)

A

white solid
white crystals on rim of test tube
thermal decomposition

38
Q

7 what happen with dehydrated copper sulfate and water

A

CuSO4 5H20 -><- CuSO4 + 5H2O
CuSO4 5H20 blue crystals
CuSO4 white crystals
water was removed when heated seen by condensation
use cobalt chloride paper to test the presence of water
paper is blue and if it turns purple/pink water is present

39
Q

8 what happens to energy transfer in a reversible reaction

A

if 50KJ was initially transferred, 50KJ will be transferred in the reversible reaction

40
Q

8 when does an open system react to

A

reacts to completion because the products can escape

41
Q

8 when does a closed system react to

A

until it reaches dynamic equilibrium because the products cannot escape
becomes reversible

42
Q

8 what is dynamic equilibrium

A

when a reversible reaction happens in a closed system the rates of the forward and backwards reactions become equal
this is equilibrium
forward and backward reactions still happen so it’s dynamic

43
Q

8 what happens the a change in equilibrium

A

when a change is made to a reaction at equilibrium, the position of equilibrium moves to oppose the change

44
Q

8 what is equilibrium position

A

gives an idea of the ratio of concentration of reactants and products

45
Q

8 when is equilibrium position on the left

A

when concentration of REACTANTS is bigger than concentration of PRODUCTS

46
Q

8 when is equilibrium position on the right

A

when concentration of PRODUCTS is bigger than concentration of REACTANTS

47
Q

8 what effect does catalysts have on equilibrium

A

no effect
it would speed up the forward and backward reactions equally so nothing changes

48
Q

8 what happens to equilibrium position when
INCREASE pressure
DECREASE pressure

A

INCREASE
- shifts to side with fewer gas molecules

DECREASE
- shifts to side with more gas molecules

49
Q

8 what happens to equilibrium position when
INCREASE concentration
DECREASE concentration

A

INCREASE
- REACTANTS shift to right
- PRODUCTS shifts to left

DECREASE
- REACTANTS shifts to left
- PRODUCTS shifts to right

50
Q

8 8 what happens to equilibrium position when
INCREASE temperature
DECREASE temperature

A

EXOTHERMIC
- INCREASE shifts to left
- DECREASE shifts to right

ENDOTHERMIC
- INCREASE shifts to right
- DECREASE shifts to left

51
Q

9 what is equilibrium yield

what does it depend on?

A

the amount of desired product is present in a reaction at equilibrium

pressure
temperature
concentration of reactants

52
Q

9 what are the considerations for using a reversible reaction

A

ROR
-needs to be as fast as possible

Yield
-dependant on equilibrium position being on the right of the reaction (favours forward reaction)

53
Q

9 how can you make ROR as fast as possible

A

use a catalysts
increase SA : V ratio
increase temperature
increase concentration or pressure

54
Q

9 how do you make methanol

A

CO + 2H2 -> CH3OH

55
Q

9 ammonia production

A

N2 + 3H2 -> 2NH3
forward reaction is exothermic so high temp would decrease ammonia yield in equilibrium

56
Q

9 what does high pressure do to ammonia

A

shift the equilibrium to the right, higher conc of ammonia in the equilibrium yield

high pressure is expensive and dangerous, so they use 200 atmospheres instead

57
Q

9 what does effervescence mean?

A

fizzing

58
Q

9 what is le chatiliers principle

A

when a change is made to a reaction at equilibrium, the position of equilibrium moves to oppose the change

Chemistry (7 decks)

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