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GCSE Chemistry > ROR notes > Flashcards

ROR notes Flashcards

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1
Q

When describing the ROR from a graph what do we always state?

A
  • The speed of the ROR
  • How is this ^ shown? + meaning (more product being formed in a given amount of time)
  • What causes this? - ie lots of reactant molecules so more frequent successful collisions so more product being formed etc.

^Always mention the frequency of collisions!

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2
Q

State collision theory:

A

Chemical reactions can only take place when the reacting particles collide with each other. The collisions must have sufficient energy.

^The sufficient energy is known as the activation energy: The minimum amount of energy that particles must have to react.

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3
Q

How do we measure the rate of reaction?

A

Amount of product formed or Amount of reactant used up/Time (s)

Product formed/Reactant used up can be measured in:

  • g (mass)
  • cm^3 (volume)
  • Moles

So rate of reaction = g/s mol/s or cm^3/s

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4
Q

What is the rate of a chemical reaction determined by?

A

The frequency of collisions of reactant molecules.

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5
Q

General rate of a chemical reaction:

A

Fast, then slows down, then stops.

This can be explain with collision theory.

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6
Q

Describe the relationship between the concentration of particles in a solution/gas and the rate of reaction.

A

Concentration is directly proportional to the rate of reaction.

If we increase the concentration of particles in a solution or in a gas, we increase the rate of reaction.

  • As the conc. increases ROR increases.
  • Because there are more reactant particles so more successful collisions/higher collision frequency.
  • So amount of reactant particles used up/product formed increases.

^This applies to gas and pressure.

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7
Q

RS of surface area and rate of reaction:

A
  • As SA increases rate increases so SA and rate are directly proportional.
  • This is bc a larger surface area means reactant particles have a higher chance of colliding with the surface of the solid reactant.

**The smaller the block of reactant, the larger the SA:Volume ratio.

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8
Q

How does temperature affect the rate of reaction?

A
  • Temperature is directly proportional to the rate of reaction.
  • As temp increases ROR increases more energy is being supplied to the reactant particles.
  • So there is an increase in the movement of particles and therefore more frequent collisions per second.
  • As the number of successful collisions per second increases, the transfer of energy between the reactant particles increases.
  • Reactant particles now have more energy to overcome the activation energy barrier.
  • So even more FQ and more reactant formed.
  • So ROR increases.
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9
Q

What are catalysts?

A

Substances that increases the rate of a chemical reaction but are not used up in them.

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10
Q

How do catalysts affect the reaction profile?

A

The reaction profile for catalysed reactions will have a lower activation energy (shown by a lower curve).

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11
Q

Why are catalysts useful?

A
  • They can be reused - because they don’t get used up in a chemical reaction.
  • They allow use to save money - because they allow use to increase the rate of the chemical reaction without increasing the temperature; this saves energy and money.
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12
Q

How do catalysts increase the rate of a chemical reaction?

A
  • They provide an alternative pathway for the reaction to occur, this pathway has a lower activation energy.
  • This means more particles, even those with low energy can cross the activation energy barrier and collide, so there are more frequent successful collisions per second.
  • So the ROR increases.
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13
Q

True or false - different chemical reactions require different catalysts?

True or false enzymes are biological catalysts?

A

True

True

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14
Q

What is meant by a reversible reaction?

A

A reaction where products can react together to produce the original reactants.

  • This is shown by the double arrow.
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15
Q

Factors which affect the rate of a reaction:

A
  • Concentration of reactions in solution.
  • The pressure of reacting gases.
  • The surface area of solid reactants.
  • The temperature of the reaction.
  • The presence of catalysts.
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16
Q

Draw a reaction profile for catalysts.

A
17
Q

An example of a reversible reaction:

A

A+B double arrow C+D

Ammonia chloride double arrow ammonia and hydrogen chloride

  • In this reaction heating causes the forward reaction and cooling causes the backward reaction.
18
Q

If a reversible reaction is endothermic in 1 direction, then in the other direction the reaction is?

A

Exothermic.

^However for each reaction the same amount of energy is transferred.

19
Q

Endothermic reaction:

Exothermic reaction:

A

Energy ENTERS - so reaction temp decreases

Energy EXITS - so reaction temp increases.

20
Q

Hydrated copper sulfate (blue)
RRS:

Forward reaction is:
Backward reaction is:

A

Anyhydrous copper sulfate (white) + Water

FORWARD = ENDO; heat
BACKWARD = EXO; cool

So if we wna get Anhydrous copper sulfate we heat and to get hydrated copper sulfate we cool.

21
Q

Anhydrous copper sulfate is:
Hydrated copper sulfate is:

A

Anhydrous copper sulfate is white
Hydrated copper sulfate is blue

22
Q

When does equilibrium occur?

A

Equilibrium occurs when a reversible reaction takes place in a sealed container which prevents any reactant and products from escaping and the forward and reverse reactions occur at the same rate.

23
Q

What is Le Chatalier’s Principle?

A

If a system is at equilibrium and a change is made to the conditions, the reaction responds to counteract the change.

24
Q

If the concentration of a reactant is increased:

A
  • The reaction is no longer at equilibrium.
  • Rate of forward reaction increases, equilibrium moves to the left.
  • So more product will be formed until equilibrium is reached again.
25
Q

If the concentration of a react is decreased:

A
  • The reaction is no longer at equilibrium
  • The rate of the backward reaction increases and the reaction moves to the left.
  • So more product will turn into reactant until equilibrium is reached again.
26
Q

If the concentration of a product is decreased:

A
  • The reaction is no longer at equilibrium
  • The rate of the forward reaction increases and equilibrium shifts to the left.
  • More reactant will react to produce the product until equilibrium is reached again.
27
Q

If the concentration of a product is increased

A
  • The reaction is no longer at equilibrium
  • The rate of the backward reaction increases, equilibrium shifts to the left
  • So more product is going to be turned into reactant until equilibrium is reached again.
28
Q

The format to answer an equilibrium question:

A
  • What is the resultant change?
  • What is the counterchange to restore equilibrium?
  • So where will equilibrium move to for this to happen and why?
29
Q

Endothermic reaction:

Exothermic reaction:

A
  • Takes in heat energy from the surroundings and the environment so the system temp decreases.
  • Releases heat energy to the surroundings and the environment so the system temp increases.
30
Q

A reaction is taking place and the forward reaction is exothermic and the backward reaction is endothermic.

Describe what will happen if the temp of the reaction is increased and decreased.

A

INCREASED TEMP:
- We need to decrease the temp
- Reaction is no longer at equilibrium
- Equilibrium will shift to the right so more product is formed.
- Because the forward reaction is exothermic so energy will be released to the surroundings until equilibrium is restored..

DECREASED TEMP:
- We need to increase the temp.
- The reaction is no longer at equilibrium
- So equilibrium will shift to the left because that reaction is endothermic so energy will be taken in from the surroundings and the system temp increases until equilibrium is restored.
- Less product is produced and more reactant is formed.

31
Q

Pressure relates to what to what substance state?

A

A gas.

32
Q

N2 + 3H2 -><(RRS) 2NH3

What happens if we increase the pressure.

A
  • The reaction will no longer be at equilibrium.
  • So to restore equilibrium, equilibrium will shift to the right
  • BC there are fewer molecules in the forward direction than the backward direction
33
Q

N2 + 3H2 -><(RRS) 2NH3

What happens if we decrease the pressure.

A
  • The reaction will no longer be at equilibrium
  • So equilibrium will shift to the left because there are more molecules in the backward direction than the forward direction.
34
Q

When the number of reactant molecules and the number of product molecules is the same, what happens to the position of equilibrium if we change the pressure?

A

Changing the pressure will have no effect on the position of equilibrium, when the number of reactant molecules is equal to the number of product molecules.

GCSE Chemistry (13 decks)

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