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Chemistry Year 11 > C8 > Flashcards

C8 Flashcards

1
Q

Activation energy

A

The minimum energy needed for a reaction to take place

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1
Q

Anhydrous

A

Describes a substance that does not contain water

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2
Q

Atmosphere

A

The relatively thin layer of gases that surround planet Earth

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3
Q

Catalyst

A

A substance that speeds up a chemical reaction by providing a different pathway for the reaction that has a lower activation energy
than the reaction without the catalyst present. With a catalyst, a higher proportion of the reactant particles have sufficient energy to react, meaning the frequency of effective collisions(collisions resulting in a reaction) and the rate of reaction speeds up.

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4
Q

Climate change

A

The change in global weather patterns that could be caused by excess levels of greenhouse gases in the atmosphere

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5
Q

Closed system

A

A system in which no matter enters/leaves

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6
Q

Equilibrium

A

The point in a reversible reaction in which the forward and backward rates of reaction are the same, so the amount of substances in the remaining mixture remain constant

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7
Q

Hydrated

A

Describes a substance that contains water in its crystals

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8
Q

Le Châtelier’s Principle

A

When a change in conditions is introduced to a reversible reaction at equilibrium, the position of equilibrium shifts(between left and right) to counteract the change

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9
Q

A reversible reaction

A

A reaction in which the products can re-form the reactants

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10
Q

Precision

A

A precise measurement where there’s very little spread about the mean value

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11
Q

Examples of slow chemical reactions

A

Rusting of iron
Chemical weathering

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12
Q

Examples of moderately quick chemical reactions

A

The metal magnesium reacting with an acid to produce a gentle stream of bubbles

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13
Q

Examples of fast chemical reactions

A

Burning
Combustion of chemicals inside a firework exploding

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14
Q

Graphs for the rate of reaction

A

Over time, the line becomes less steep as the reactants are used up.
If graphs meet(converge) at the same level, they all produce the same amount of product although they take different times to produce it.

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15
Q

Rate of a chemical reaction

A

How fast the reactants are turned into products

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16
Q

How the collision theory impacts the rate
of reaction

A

The more collisions there are the faster the reaction is. Particles have to collide with enough energy for the collision to be successful.

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17
Q

Collision frequency

A

How often reacting particles collide
with enough energy to cause a reaction to take place

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18
Q

Factors affecting rates of reaction

A

Temperature
Concentration of solution/pressure of as
Surface area of solids
Presence of a catalyst
These all increase the number of successful collisions between the reacting particles, which increases the rate of reaction.

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19
Q

How does temperature affect the rate of reaction?

A

When the temperature is increased, energy is transferred to particles, so particles move faster, so collide with more frequently and enough energy for the reaction to occur.
Here, an increased proportion of particles exceeding the activation energy will have a greater effect on rate than the increased frequency of collisions.

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20
Q

How does concentration/pressure affect the rate of reaction?

A

If a solution is made more concentrated, there are more particles knocking about in the same volume of water and when the gas pressure increases, the same number of particles occupy a smaller space and the reactant particles are more crowded together, making collisions more frequent and likely

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21
Q

How does surface area affect the rate of reaction?

A

If one of the reactants is a solid, breaking it into smaller pieces means the particles around it have more area to work one - so there will be more frequent collisions. The larger the surface area to volume ratio, the faster the reaction.

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22
Q

How does using a catalyst affect the rate of reaction?

A

Catalysts decrease the activation energy needed for the reaction to occur by providing an alternative reaction pathway with a lower activation energy. Catalysts speed up the reaction and increase the rate of reaction

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23
Q

Rate of reaction=

A

Amount of reactant used/product formed divided by time

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24
Q

How to measure the rate of reaction using precipitation and colour change?

A

1)Can record visual change in reaction if the initial solution is transparent and the product is an opaque precipitate(clouding the solution).
2) Observe a mark through the solution and measure how long it takes for it to disappear - the faster the mark disappears, the quicker the reaction.
3) If the reactants are coloured and the products are colourless, you can time how long it takes for the solution to lose/gain its colour.

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25
Q

Disadvantages of measuring rate of reaction using precipitation and colour change?

A

Subjective results - people might not agree on point where mark disappears/solution changes colour
Can’t plot a rate of reaction graph from the results

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26
Q

How to use change of mass to measure the rate of reaction?

A

1) A mass balance is used to measure the speed of reaction producing a gas.
2) As a gas is released, the mass disappearing is measured on the balance.
3) The quicker the reading on the balance drops, the faster the reaction. This shows as the reaction takes place, the mass of the reaction mixture decreases. You can measure and record the mass at regular time intervals.
Safety: Wear eye protection
Equipment:
Cotton wool bung - putting cotton wool in the top of the flask lets the gas escape, but stops the acid spitting out
Marble chips and hydrochloric acid
Conical flask

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27
Q

Advantages of using changes in mass to measure the rates of reaction?

A

Most accurate of three methods due to mass balance.
If you take measurements at regular intervals, you can plot a rate of reaction graph

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28
Q

Disadvantages of using changes in mass to measure the rate of reaction?

A

Could release the gas straight into the room

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29
Q

How to use the volume of gas to measure the rate of reaction?

A

1) Can use a gas syringe to measure the volume of gas given off.
2) The more gas given off during a given time interval, the faster the reaction

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30
Q

Advantages of using the volume of gas to measure the rate of reaction?

A

Gas syringes are easier to read accurately and more precise
Can take measurements at regular intervals and plot a rate of reaction graph

31
Q

Disadvantages of using the volume of gas to measure the rate of reaction?

A

If the reaction is too vigorous, you could blow the plunger out of the end of the syringe
You could record loss of mass more accurately than volume of gas
Make repeat measurements and calculate mean values

32
Q

Required practical: using magnesium and hydrochloric acid to measure the effect of concentration on the rate of reaction.

A

1) Add a set volume of dilute hydrochloric acid to a conical flask - place on a mass balance.
2) Add some magnesium ribbon to the acid - plug the flask with cotton wool.
3) Start the stopwatch, take readings of the mass from the balance at regular intervals, plot the results in a table and work out the mass lost for each reading.
4) Plot this in a graph, but repeat the experiment with more concentrated acid solutions.

33
Q

Control variables when using magnesium and hydrochloric acid to measure how concentration changes the rate of reaction

A

Amount of magnesium ribbon
Volume of acid

34
Q

Required practical: using sodium thiosulfate and hydrochloric acid to measure the rate of reaction

A

1)
These two chemicals are clear solutions which react to form a yellow precipitate of sulfur.
2) Start by adding a set volume of dilute sodium thiosulfate to a conical flask.
3) Place the flask on a piece of paper with a black cross, add some dilute hydrochloric acid to the flask and start the stopwatch.
4) Watch the black cross disappear through the cloudy sulfur and time how long it takes to go
5) The reaction can be repeated using solutions of either reactant at different concentrations

35
Q

Control variables when using sodium thiosulfate and HCL to see how concentration affects the rate of reaction

A

The depth of the liquid

36
Q

Disadvantages of using sodium thiosulfate and HCL to measure how concentration affects the rate of reaction

A

Doesn’t give a set of graphs

37
Q

Why will reversible reactions reach equilibrium?

A

As reactants react, their concentrations fall, so the forward reactions slow down. But as more products are made and their concentrations rise, the backward reaction will speed up(the rate at which they react to re-form reactants). After a while, the forward reaction will be going at exactly the same rate as the backward one, but in opposite directions.

38
Q

Dynamic equilibrium

A

Where both reactions are still happening, but there’s no overall effect, meaning the concentrations of reactants and products have reached a balance and won’t change

39
Q

Condition for equilibrium

A

Equilibrium’s only reached if the reversible reaction occurs in a closed system

40
Q

What does it mean if the equilibrium lies to the right?

A

The concentration of products is greater than that of the reactants

41
Q

What does it mean if the equilibrium lies to the left?

A

The concentration of reactants is greater than that of the products

42
Q

What affects the position of equilibrium?.

A

Temperature
Pressure(only with equilibrium in gases)
The concentration of the reactants and products

43
Q

Are reversible reactions endothermic or exothermic?

A

In reversible reactions, if the reaction is endothermic in one direction, it will be exothermic in the other. This is because energy can’t be created or destroyed in a chemical reaction.

44
Q

How do changes of the temperature show Le Chatelier’s Principle?

A

If you decrease the temperature, the equilibrium moves in the exothermic direction to produce more heat, so you’ll get more products for the exothermic reaction and fewer products for the endothermic reaction.
If you raise the temperature, the equilibroum moves in the endothermic direction to decrease it: you’ll get more products for the endothermic reaction than for the exothermic reaction.

45
Q

How do changes in pressure show Le Chatelier’s theory?

A

If you increase the pressure, the equilibrium reduces it by moving in the direction where there are fewer molecules of gas.
If you decrease the pressure, the equilibrium increases it by moving innthe direction with more molecules of gas.

46
Q

How do changes in concentration show Le Chatelier’s principle?

A

If you increase the concentration of the reactants the system decreases it by making more products.
If you decrease the concentration of products the system tries to increase it by reducing the amount of reactants.

47
Q

Two ways to work out the rate of a chemical reaction

A

You can find out how quickly:
The reactants are used up as they make products
The products of the reaction are made

48
Q

When are reactions more likely to happen hetween reactant particles:

A

If you:
Increase the frequency of reacting particles colliding with each other.
Increase the energy reactant particles have when they collide
When a higher proportion of particles have sufficient energy above the activation energy to react

49
Q

What affects the rate of reaction when a solid reacts in a solution?

A

The particles inside a large lump of solud are not in contact with the reactant particles in the solution, so they can’t react.
In smaller lumps, each tiny piece of solid is surrounded by solution: many more particles of the solid are able to react at a given time, so reactions occur quickly

50
Q

How does the size of an object link to its surface area to volume ratio?

A

The smaller the size of the pieces of a solid material, the larger its surface area to volume ratio. As the side of a cube decreases in size by a factor of 10, its surface area to volume ratio increases by 10.

51
Q

Mean rate of reaction=

A

(Quantity of reaction used/product formed)/Time

52
Q

Why are buildings made of limestone and marbe crumbling away?

A

Because both limestone and marble are mainly calcium carbonate, which reacts with acids, leaving the stone soft and crumbly. The rate of reaction will speed up, because the concentration of acids in rainwater has increased.

53
Q

Required practical: investigating the effect of changing concentration on the rate of reaction by reacting marble chips with different concentrations of hydrochloric acid

A

1) You can find the rate of reaction by plotting the volume of carbon dioxide gas given off as the reaction progresses over time. You can measure the volume of gas at regular time intervals.

54
Q

Examples of most effective catalysts

A

Gold
Platinum
Palladium

55
Q

How to investigate the effect of different catalysts on a rate of reaction(practical)

A

1) Reaction example: hydrogen peroxide decomposing
2) The reaction produces oxygen gas, you can collect this using a gas syringe into a conical flask.
3)You can investigate the effect of many different substances on the rate of this reaction(e.g. manganese oxide and potassium iodide).
4) A table of the time taken to produce a certain volume of oxygen can tell you which catalyst makes the reaction go fastest.
Safety: Wear eye protection. If the syringe is glass, try and ensure the piston doesn’t fall out and break. Manganese oxide is harmful.

56
Q

Advantages of catalysts in industry

A

Cheaper to use a catalyst than to pay for the extra energy needed without one.
Operating at lower temperatures and pressures conserves non-renewable energy resources/fossil fuels and stops CO2 entering the atmosphere when fossil fuels are burnt, helping to combat climate change.

57
Q

Examples of reversible reactions

A

Trying to neutralise an alkaline solution with an acid
Salts and their water of crystallisation
When tou heat ammonia chloride, it thermally decomposes into ammonia gas and hydrogen chloride gas and these hot gases rise up the test tube, but when they cool down near the mouth of the tube, they react with each other. The gases re-form ammonium chloride again.

58
Q

Reversible reaction when blue copper sulfate crystals are heated

A

1) The copper sulfate is hydrated - the crystals contain water as part of the lattice formed when the copper sulfate crystallised.
2) Heating the copper sulfate drives off the water from the crystals, producing white anhydrous copper sulfate(endothermic reaction).
3)When you add water to anhydrous copper sulfate, hydrated copper sulfate is formed. The reaction in this direction is exothermic. The colour change in this reaction, from white to blue,is a useful test for the presence of water.

59
Q

How to test for the presence of water

A

1) You can soak filter paper in cobalt chloride solution and allow it to dry in an oven.
2) The blue paper that is produced is called cobalt chloride paper.
3) The paper turns pale pink when water is added to it, so can be used as an indicator for the presence of water.

60
Q

How to measure energy changes in a reversible reaction

A

1) Gently heat a few copper sulfate crystals in a test tube. Observe the changes.
2) When the crystals are completely white, allow the tube to cool to room temperature(this takes several minutes).
3) Add two or three drops of water from a dropper and observe the changes. Carefully feel the bottom of the test tube and explain the changed gou have observed.
Safety:
Wear eye protection.
Copper salts are harmful.

61
Q

How does altering the pressure affect the equilibrium mixture?

A

If the forward reaction produces more molecules of gas, an increase in pressure decreases the amount of products formed and a decrease in pressure increases the amount of products formed.
If the forward reaction produces fewer molecules of gas, an increase in pressure increases the amount of products formed and a decrease in pressure decreases the amount of products formed.

62
Q

How does pressure affect the composition of the equilibrium mixture when there are equal numbers of gas molecules on both sides of the equation?

A

Changing the pressure has no effect on the composition of the equilibrium mixture, but increasing
the pressure will speed up both the forward and reverse reactions by the same amount.

63
Q

How does changing the temperature affect the amount of products and reactants formed in a reaction?

A

If the forward reaction is exothermic, an increase in temperature decreases the amount of products formed and a decrease in temperature increases the amount of products formed.
If the forward reaction is endothermic, an increase in temperature increases the amount of products formed and a decrease in temperature decreases the amount of product formed.

64
Q

Required practical: using sodium thiosulfate and hydrochloric acid to measure the rate of reaction(how to improve method)

A

Use a light sensor

65
Q

Which solvent is commonly used to dissolve ions?

A

Water

66
Q

Effect of using catalysts in equilibrium

A

No effect/change on equilibrium yields

67
Q

Catalyst for nitric acid

A

Platinum

68
Q

What happens to catalysts used in chemical plants?

A

They eventually become poisoned, because impurities in the reaction mixture combine with the catalyst and stop it working properly

69
Q

How this the steepness of the graph affect the rate of reaction?

A

The steeper the graph, the faster the reactio

70
Q

Reaction-mixture of acid and sodium thiosulfate(disappearance of cross)

A

Na2S2O3(aq)+ 2HCl(aq): 2NaCl(aq)+ SO2(g) + S(s)+ H2O(l)

71
Q

Method used cor marble chips and acid(measuring mass loss)

A

1) Weight 10g of marble chips on a mass balance
2) Place marble chips into a flask.
3)Measure 50cm3 of hydrochloric acid with a measuring cylinder.
4) Pour hydrochloric acid into the flask, connect a gas syringe and start a timer.
5) Record the volume of gas produced every 10 seconds

72
Q

Marhle chips(CaCO3) + acid reaction:

A

CaCO3(s)+ 2HCl(aq): CaCl2(aq)+ CO2(g) + H2O(l)

73
Q

What happens if the concentration of reactants increased?

A

The position of equilibrium shifts towards products so more product is produced until equilibrium is reached again

74
Q

What happens if the concentration of products is increased?

A

The position of equilibrium shifts towards reactants so more reactant is produced until equilibrium is reached again

75
Q

Effect of pressure changes on equilibrium

A

If pressure is increased, equilibrium shifts to side of equation with
fewer moles of gas(e.g. equilibrium moves right as there are fewer moles of gas on the right hand side, forming more product)
If pressure is decreased, equilibrium will shift to side of equation with more moles of gas(e.g. equilibrium would move left, making more reactants)

Chemistry Year 11 (12 decks)

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