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GCSE CHEMISTRY > P2- The rate and extent of chemical change > Flashcards

P2- The rate and extent of chemical change Flashcards

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1
Q

What is the rate of a chemical reaction?

A

How fast the reactants are changed into the products

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2
Q

2 examples of slow rates of reaction

A

1) Iron rusting
2) Chemical weathering (acid rain damage)

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3
Q

1 example of a moderate rate of reaction

A

Magnesium reacting with an acid to produce a gentle stream of bubbles

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4
Q

1 example of a very fast rate of reaction

A

Explosions

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5
Q

The steeper the line on a graph…

A

The faster the rate of reaction

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6
Q

Why do the lines on the graph becomes less steep over time?

A

The reactants are used up

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7
Q

2 things a line on a graph would have if it was a very fast reaction

A

1) Steepest line
2) Become flat in the least time

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8
Q

What does it mean if different lines on a graph all converge at the same level?

A

They all produce the same amount of products but take different times to produce it

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9
Q

2 things the rate of a chemical reaction depends on?

A

1) The collision frequency of particles
2) The energy transferred during a collision

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10
Q

If there are more collisions, will the rate of reaction be faster or slower

A

Faster

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11
Q

What is activation energy?

A

The minimum amount of energy particles need to react

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12
Q

What do particles need activation energy for?

A

To break the bonds in the reactants and start the reaction

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13
Q

2 ways to calculate the mean rate of reaction

A

Either ‘Quantity of reactants used’ or ‘Quantity of products formed’ divided by time taken

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14
Q

5 factors that increase rate of reaction

A

1) Temperature
2) Concentration
3) Pressure
4) Surface area
5) Adding a catalyst

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15
Q

What is ‘Collision theory’?

A

It explains how various factors affect the rate of reaction . For chemical reactions to occur, particles must collide with each other and with minimum energy

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16
Q

How does temperature increase rate of reaction?

A

1) Temp increased= particles have more energy
2) Means they vibrate more, so more likely to collide
3) When they collide they have more energy and it is more frequent

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17
Q

How does concentration increase rate of reaction?

A

1) Increasing concentration= more particles in given volume
2) More likely to collide as there are more particles (increased frequency)
3) More collisions= more likely to be successful

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18
Q

How does pressure increase rate of reaction?

A

1) Increasing pressure= same number of particles in smaller amount of space
2) More likely to collide as particles are closer together
3) More collisions= more likely to be successful

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19
Q

How does surface area increase rate of reaction?

A

1) Increased SA= particles are more exposed
2) More likely to collide= more frequent collisions
3) Collisions more likely to be successful

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20
Q

How does adding a catalyst increase rate of reaction?

A

1) Decrease the activation energy needed for the reaction to occur
2) They do this by providing an alternative pathway with a lower activation energy
3) They are not used up in the process

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21
Q

When can you record the visual change in a reaction?

A

If the initial solution is transparent and the product is a precipitate which clouds the solution (becomes opaque)

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22
Q

Change in mass practical steps

A

1)We can measure the speed of a reaction that produces a gas by using a mass balance
2) As gas is released, the mass disappearing is measured on the balance
3) Quicker the reading on the balance drops, the faster the reaction
4) If you take measurements at regular intervals, you can plot a rate of reaction graph and find the rate quite easly

23
Q

Volume of gas given off practical steps

A

1) Involves using a gas syringe to measure volume of gas given off
2) More gas given off during a given time interval= faster the reaction
3) You can take measurements at regular intervals and plot a rate of reaction graph

24
Q

What are the 2 practical experiments that measure the effect of concentration on the rate of reaction

A

1) Magnesium and Hydrochloric acid to produce Hydrogen gas (H2)
2) Sodium thiosulfate and Hydrochloric acid to produce a cloudy precipitate

25
Q

Magnesium and HCl experiment steps

A

1) Add a set volume of dilute HCl to a conical flask and place on a mass balance
2) Add some magnesium ribbon to the acid and plug the flask with cotton wool
3) Start stopwatch and record mass on the balance at regular intervals
4) Plot results in a table to work out mass lost for each reading
5) Repeat with more concentrated acid solutions (only thing that should change)

26
Q

Sodium thiosulfate and HCl experiment steps

A

1) Add a set volume of dilute sodium thiosulfate to conical flask
2) Place flask over black cross, add dilute HCl and start the stopwatch
3) Watch cross disappear through the cloudy sulfur and time it
4) Repeat with solutions of either reactant at different concentrations
5) This experiment doesn’t give a set of graphs just a reading

27
Q

How to work out mean rate of reaction from a graph

A

Find the gradient (change in y/ change in x)

28
Q

How do you work out the rate of reaction at a particular point?

A

Draw a tangent at the particular point and then work out the gradient from there

29
Q

What is a reversible reaction?

A

The products can react together to make the original reactants again

30
Q

What is an irreversible reaction?

A

The reactants react completely to form the products

31
Q

If a forward reaction is exothermic, what is the backwards reaction?

A

Endothermic

32
Q

If the forward reaction requires heating, what will the backwards reaction require?

A

Cooling

33
Q

What is a system in equilibrium?

A

The forward reaction is going at the exact same rate as the backwards reaction

34
Q

When a system is in equilibrium, what happens to the concentration?

A

The concentrations of the reactants and products have reached a balance and won’t change

35
Q

what does the reversible reaction have to take place in to reach equilibrium?

A

A closed system

36
Q

What is a closed system?

A

None of the reactants or products can escape and nothing else can get in

37
Q

When a system is in equilibrium are the reactants and products equal?

A

No

38
Q

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

A

The concentration of products in greater than that of the reactants

39
Q

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

A

The concentration of reactants in greater than that of the products

40
Q

3 factors that affect the position of equilibrium?

A

1) Temperature
2) Pressure
3) Concentration

41
Q

What is Le Chatelier’s Principle?

A

The idea that if you change the conditions of a reversible reaction at equilibrium, the system will try and counteract that change.

42
Q

How does an increase in temperature affect the position of equilibrium?

A

The equilibrium will shift to the endothermic direction as this takes in the excess heat and restores equilibrium

43
Q

How does a decrease in temperature affect the position of equilibrium?

A

The equilibrium will shift to the exothermic direction as this releases heat and restores equilibrium

44
Q

If the temperature change is negative, is the reaction endo or exothermic?

A

Exothermic, on forward reaction

45
Q

If the temperature change is positive, is the reaction endo or exothermic?

A

Endothermic, on forward reaction

46
Q

How does increasing pressure affect the position of equilibrium?

A

The equilibrium tries to reduce it by shifting to the side with fewer moles of gas

47
Q

How does decreasing pressure affect the position of equilibrium?

A

The equilibrium tries to increase it by shifting to the side with more moles of gas

48
Q

Changing pressure only affects equilibrium under what state?

A

Gases

49
Q

How does increasing the concentration of a reactant affect the position of equilibrium?

A

The equilibrium shifts to the side of the products

50
Q

How does increasing the concentration of a product affect the position of equilibrium?

A

The equilibrium shifts to the side of the reactants

51
Q

How does decreasing the concentration of a reactant affect the position of equilibrium?

A

The equilibrium shifts to the side of the reactants

52
Q

How does decreasing the concentration of a product affect the position of equilibrium?

A

The equilibrium shifts to the side of the products

53
Q

Will a catalyst alter the position of equilibrium/ the composition of equilibrium?

A

No

54
Q

2 things catalysts speed up in reactions in equilibrium

A

1) Speeds up rate of both forward and backward reactions equally
2) Increases the rate at which equilibrium is reached

GCSE CHEMISTRY (10 decks)

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