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GCSE Chemistry paper 2 > The Rate and Extent of Chemical Change > Flashcards

The Rate and Extent of Chemical Change Flashcards

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1
Q

What is rate of reaction?

A

How fast reactants are changed into products.

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2
Q

What is an example of a very slow reaction?

A

Iron rusting/ chemical weathering like erosion.

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3
Q

What is an example of a moderate reaction?

A

Magnesium reacting with an acid to produce a constant stream of bubbles.

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4
Q

What is an example of a fast reaction?

A

Burning or explosion.

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5
Q

How can you tell how fast a reaction is from a graph?

A

The steeper the gradient the higher the rate of reaction.

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6
Q

What the collision theory?

A

Rate of reaction depends on:

  • The collision frequency of particles in a reaction,
  • The energy transferred during a collision.
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7
Q

What is activation energy?

A
  • The minimum amount of energy needed for a reaction, - Particles need this much energy to break the bonds in the reactants to start the reaction.
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8
Q

How do you increase the rate of reaction?

A
  • Increase number of collisions,
  • Increase the amount of energy transferred per collision.
    This can be done by increasing one of the factors of rate of reaction.
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9
Q

Factors effecting rate of reaction?

A
  • Temperature,
  • Surface area,
  • The concentration of a solution or the pressure of gas,
  • The presence of a catalyst
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10
Q

How does increased temperature increase the rate of reaction?

A
  • Particles have more energy so move faster and collide more,
  • This means more energy for the reaction because there are more collisions.
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11
Q

How does increased Surface area increase the rate of reaction?

A
  • There are more collisions if there is more area for particles to hit each other.
  • This means more energy for the reaction from more collisions.
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12
Q

How does increased Concentration/ pressure increase the rate of reaction?

A
  • There are more particles if the pressure/ concentration is increased,
  • So more collisions take place,
  • More collisions mean more energy in the reaction.
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13
Q

How does Using a catalyst increase the rate of reaction?

A
  • Catalysts speed up reaction by finding an alternate route for reactions,
  • This lowers the amount of activation energy so the reaction happens quicker.
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14
Q

What is the equation for rate of reaction?

A

Rate of reaction = Amount of reaction used or amount of product formed/ time

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15
Q

What are the three ways to measure the rate of reaction:

A
  • Precipitation/ change in colour (visual change),
  • Change in mass (Mass can decrease if gas is produced/ reactants react with air),
  • The volume of gas given off (The gas can be measured in a syringe).
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16
Q

How can you test for the correlation between rate of reaction and concentration of an acid (involving HCL and Mg strips)?

A
  • Pour a set volume of Hydrochloric acid into a conical flask, with a known concentration,
  • Put the conical flask on a scale and take the mass
  • Add a magnesium strip to the conical flask and instantly plug the flask with cotton wool,
  • Measure the change in mass over regular intervals and plot it on the graph,
  • Do the same with different concentrations of hydrochloric acid.
17
Q

How can you test for the correlation between rate of reaction and concentration of an acid (involving HCl and Sodium thiosulfate)?

A
  • Pour a set volume of clear Sodium thiosulfate into a conical flask,
  • The conical flask should be over a black cross on the table,
  • Then add HCl to the solution (of a known concentration), and start a timer,
  • The solution should start to turn yellow, stop the timer when you can no longer see the cross,
  • This is the rate of reaction, it can be compared to the same reaction redone, but with different concentrations of HCl,
  • You should see that a higher concentration means a higher rate of reaction.
18
Q

How do you find the average gradient of a curve?

A

Draw a tangent and find the gradient of the tangent.

19
Q

How do reversible reactions work?

A
  • Two reactants will react together to create a product or a few products,
  • This product will then turn back into the reactants,
  • Both the reactants and products turn into each other, the reactants originally react faster because there are less products at the start of the reaction, so less reaction take place (products -> reactants)
  • Eventually, they will react at the same rate and create an equilibrium,
  • Equilibrium only takes place when the reaction takes place in a closed system.
20
Q

How can the positioning of the equilibrium change?

A
  • The positioning of the equilibrium is never in the middle,
  • If the equilibrium is on the right, it means there is a greater concentration of reactants,
  • If the equilibrium is on the left, it means there is a greater concentration of products,
21
Q

What factors effect the position of the equilibrium?

A
  • There are three factors which can move the equilibrium right to left:
  • Temperature,
  • The pressure,
  • The concentration of the reactants and products.
22
Q

What is a catalyst?

A

Catalysts speed up rate of reaction by finding an alternate route for reactions that have a lower activation energy, but are not used up in the reactions.

23
Q

Why don’t we include catalysts in chemical equations?

A

They are not used up in reactions so do not count as reactants.

24
Q

If one reaction in a reversible reaction is exothermic, what will the other be?

A

Endothermic, the same amount of energy is transferred both ways though.

25
Q

What is equilibrium?

A

When the two reversible reactions are reacting at the same rate.

26
Q

What is Le Chatelier’s principle?

A

If a system is at equilibrium and a change is made to the conditions, then the system will respond to counteract the change.

A bit like negative feedback.

27
Q

What happens if you increase concentration of reactants to one side of the equilibrium of a reversible reaction?

A
  • The reaction that had added reactants will react faster, so is no longer at equilibrium,
  • The reactions will eventually balance out as more reactants become more products and reach equilibrium again,
  • This uses Le Chatelier’s principle.
28
Q

What happens if the temperature of a system at equilibrium is increased?

A
  • The equilibrium shifts to the side of the endothermic reaction because it absorbs energy,
  • This will reduce the temperature of the system,
  • So, the amount of endothermic products would increase and the amount of exothermic products would decrease in order to keep the temperature as it was before.
29
Q

What happens if the temperature of a system at equilibrium is decreased?

A
  • The equilibrium shifts to the side of the exothermic reaction as more heat energy has to be released,
  • This will raise the temperature back to normal,
  • This means that there will be more exothermic products and less endothermic products, in order to keep the systems temperature the same.
30
Q

What is pressure?

A

The number of gas molecules in a certain area.

31
Q

What does the pressure of a gas depend on?

A
  • The number of molecules,
  • Temperature,
  • Volume of container.
32
Q

What happens if we increase the pressure on a reversible reaction at equilibrium?

A

The position of the equilibrium shifts to the side with a smaller number of molecules.

33
Q

What happens if we reduce the pressure on a reversible reaction at equilibrium?

A

The position of the equilibrium shifts to the side with a larger number of molecules.

34
Q

What happens if pressure is changed when both sides of an equilibrium have the same number of molecules?

A

No effect.

GCSE Chemistry paper 2 (5 decks)

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