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Chemistry > Chapter 6 - The Rate and Extent of Chemical Change > Flashcards

Chapter 6 - The Rate and Extent of Chemical Change Flashcards

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1
Q

What is rate of reaction?

A

How fast the reactants are turned into products

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2
Q

What is the equation for mean rate of reaction?

A

Reactant used/product formed divided by time taken

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3
Q

What are the factors that affect rate of reaction?

A
  • Surface area of reactants
  • Temperature
  • Concentration (for liquids)
  • Pressure (for gases)
  • Catalysts
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4
Q

What two things must happen for a chemical reaction to occur?

A
  • Reactants must collide

- Reactants must have enough energy

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5
Q

What is the effect of concentration on rate of reaction?

A

The higher the concentration the more particles there are in a given volume, so it is more likely that particles collide and react - more frequent collisions which results in faster reaction

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6
Q

Explain collision theory (what is a successful collision)

A
  1. Two pairs of particles move towards each other
  2. Pairs collide and reform so each member of the original pair joins with a member of the other pair. This forms two new pairs
  3. The new pairs move away from each other
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7
Q

What is activation energy?

A

The minimum energy needed for particles to be able to react

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8
Q

What is the link between rate of reaction and frequency of successful collisions?

A

Directly proportional

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9
Q

What is the effect of the surface area on rate of reaction?

A

The larger the surface area the faster the rate of reaction because there are more particles able to react meaning there are more collisions

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10
Q

What is the effect of temperature on rate of reaction?

A
  • Increasing the temperature gives the particles more energy so they move faster meaning there is a higher frequency of collisions
  • More particles have energy greater than the activation energy so there are more successful collisions
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11
Q

What are the ways you can measure the formation of product?

A
  • Precipitation (colourless to cloudy) - disappearing cross method
  • Change in mass using a balance (gas is formed)
  • Volume of gas given off (collect gas in a gas syringe)
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12
Q

Pros and cons of disappearing cross method

A 
Pros:
-simple
-easy
Cons:
-subjective
-only works for visual change
-can't plot rate
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13
Q

Pros and cons of measuring change in mass using balance

A 
Pros:
-accurate
Cons:
-releases gas into room
-some gases won't weigh enough to be picked up (would need to increase resolution)
-only use when gas is given off
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14
Q

Pros and cons of collecting gas with a gas syringe

A

Pros;
-sensitive (gives very accurate results)
-gas isn’t released into the room
Cons:
-don’t get bung on quick enough (human error)
-if reaction is too vigorous you could blow plunger out of the syringe
-only use for gases

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15
Q

What is a catalyst?

A

A substance which speeds up the rate of reaction without being used up. It does this by lowering the activation energy of the reaction.

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16
Q

Many catalysts are … ?

A

Transition metals

17
Q

What effect do catalysts have on rate of reaction?

A

Catalysts will increase the frequency of successful collisions because they lower the activation energy meaning more particles have energy greater than the activation energy

18
Q

What is a reversible reaction?

A

The reactant can turn into the products and the products can turn back into the reactants

19
Q

What do we call the reaction that goes from reactants to products (arrow to the right)

A

Forward reaction

20
Q

What do we call the reaction that goes from products to reactants (arrow to the left)

A

Backward reaction

21
Q

What factors can determine the direction of the reaction?

A
  • Temperature
  • Pressure
  • Amount of reactants/products (volume)
  • Concentration
22
Q

How are the energy changes in a reversible reaction balanced?

A
  • energy released in one direction = energy absorbed in other direction
  • if forward reaction is exothermic then the backward reaction is endothermic and vice versa
23
Q

What is dynamic equilibrium?

A
  • Rate of forward reaction = rate of backward reaction
  • No observable change but reactions are occuring in both directions
  • Both reactants and products present
  • Concentration and amount of products and reactants aren’t always equal
24
Q

What is needed for a dynamic equilibrium?

A
  • Reversible reaction

- Closed system

25
Q

What is an open system and closed system?

A

Open system = heat and matter can leave

Closed system = only heat can leave

26
Q

What do we call it when there are more reactants than products and vice versa?

A

More reactant: the reaction lies to the left (like the chemical equation)
More product: lies to the right

27
Q

If the conditions change the equilibrium becomes unstabilised. What are these conditions/stresses?

A
  • Temperature
  • Concentration
  • Pressure
  • Amount of reactant
28
Q

What is Le Chatelier’s principle?

A

Whatever you do to a reaction at equilibrium, the equilibrium will move to oppose the change e.g. make it hotter then equilibrium moves to cool it

29
Q

What happens if you add more reactant (higher concentration) to a reaction in dynamic equilibrium?

A

The equilibrium will shift to the right so more product will be formed.

30
Q

What happens if you remove product (lower concentration) from a reaction in dynamic equilibrium?

A

The equilibrium will shift to the right so there’ll be less reactant as it would be used to produce more of the products

31
Q

What happens if you cool a reaction in dynamic equilibrium?

A

The equilibrium will shift to oppose the change and the exothermic would be favoured (shift towards the products of the exothermic reaction).

32
Q

What happens if you heat a reaction in dynamic equilibrium?

A

The equilibrium will shift to oppose the change and the endothermic would be favoured (shift towards the products of the endothermic reaction).

33
Q

What happens if you increase the pressure of a reaction in dynamic equilibrium?

A

Equilibrium will shift to the side with less gas molecules to reduce the pressure.

34
Q

What happens if you decrease the pressure of a reaction in dynamic equilibrium?

A

Equilibrium will shift to the side with more gas molecules to increase the pressure

35
Q

What happens if you increase the pressure of a reaction in dynamic equilibrium where the reactants and products have equal pressure?

A

The equilibrium will not be affected but the rate of both the forward and backward reaction would speed up

36
Q

What happens if you add a catalyst to a reaction in dynamic equilibrium?

A
  • does not affect equilibrium (no shifts)

- increases rate of forward and backward reaction

Chemistry (11 decks)

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