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chemistry > 6. Rate and Extent of Chemical Change > Flashcards

6. Rate and Extent of Chemical Change Flashcards

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1
Q

What is the rate of reaction?

A

The rate of reaction is a measure of how quickly a reaction takes place and how fast reactants turn into products

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2
Q

Give the 2 equations used to calculate the rate of reaction

A

mean rate of reaction = quantity of reactants used / time taken
mean rate of reaction = quantity of product formed / time taken

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3
Q

Give 3 ways the units for the rate of reaction can be measured?

A
  • g/s
  • cm3/s
  • moles/s
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4
Q

How can we measure the rate of reaction on a graph?

A

By drawing a tangent to the curve and finding the gradient

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5
Q

Why would the rate of reaction decrease as time passes?

A

A lot of the reactant molecules have already reacted and turned into products, so there are fewer reactant molecules available to react

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6
Q

What does it mean if the rate of reaction stops?

A

All of the reactant molecules have reacted

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7
Q

What does the collision theory state?

A

The collision theory states that chemical reactions occur only when reactant particles collide with each other and collide with sufficient energy to react

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8
Q

COLLISION THEORY:

What is needed in order for chemical reactions to take place?

A
  • Reactant particles have to collide into each other
  • Have enough energy to cause a reaction
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9
Q

What 4 factors affect the rates of chemical reactions

A
  • The concentrations of reactants in the solution or the pressure of reacting gases
  • The surface area of solid reactants
  • The temperature
  • The presence of catalysts
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10
Q

COLLISION THEORY

What do the 4 factors affecting the rate of chemical reactions increase?

A
  • The frequency of reacting particles colliding with each other
    OR
  • The energy they have when they collide
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11
Q

What is activation energy?

A

Activation energy is the minimum amount of energy that particles must have to react

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12
Q

Explain what effect increasing the concentration has on the rate of reaction?

A
  • Increasing the concentration of a solution will increase the rate of reaction
  • This is because there will be more reactant particles moving around in a given volume
  • The more “crowded together” the reactant particles are, the more likely they will collide
  • This results in more frequent collisions, increasing the rate of reaction
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13
Q

Explain what effect increasing the pressure has on the rate of reaction?

A
  • Increasing the pressure means that the gas particles are squashed closely together
  • This means that there are more gas particles in a smaller space
  • This increases the chance they will collide and react
  • This produces more frequent collisions, which increases the rate of reaction
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14
Q

Give 2 ways how increasing the temperature of the reactant increases the rate of reaction?

A
  • Increasing temperature causes particles to collide more frequently
  • Increasing temperature causes particles to collide with more energy
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15
Q

Explain how increasing the temperature increases the frequency of collisions?

How does it increase the rate of reaction?

A
  • Increasing the temperature means that the particles will have more kinetic energy
  • This means that particles in a solution or gas will move around faster
  • So they will collide more frequently and increase the frequency of collisions, which gives them more chances to react
  • This increases the rate of reaction
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16
Q

Explain how increasing the temperature causes particles to collide with more energy?

How does it increase the rate of reaction?

A
  • Increasing the temperature means that the particles are moving around quickly with more energy
  • This means that any collision they have will be more energetic
  • This means that a higher proportion of particles will have energy greater than the activation energy and will result in a reaction taking place
  • Overall, it increases the rate of collisions that are successful

e.g. think of two people colliding when running rather than walking

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17
Q

Explain what effect increasing the surface area has on the rate of reaction?

A
  • Increasing the surface area means that more particles are exposed to the other reactant
  • This means that more particles can react at the same time
  • This increases the frequency of collisions which increases the rate of reaction
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18
Q

Describe the SA : V ratio for small pieces of powder

A

The smaller the sizes of the pieces, the larger the SA : V ratio

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19
Q

What are catalysts?

A

Catalysts are substances which speed up the rate of a reaction without being used up in it

Benefit: Can be reused

20
Q

____________ catalysts are needed for ____________ reactions

A

Different catalysts are needed for different reactions

21
Q

How do catalysts function?

A

Catalysts increase the rate of reaction by providing an alternative reaction pathway to the products, with a lower activation energy

22
Q

Catalyst Diagram

A
23
Q

Name 2 ways we can identify the catalyst in a reaction?

A
  • Their effect on the rate of reaction
  • They are not included in the chemical equation for the reaction, as they are neither reactants nor products
24
Q

Why are catalysts not included in the chemical equation for the reaction

A

Catalysts are not included in the chemical equation for the reaction as they are not used up in the reaction

25
Q

Why do industries use catalysts?

A

Industries use catalysts to increase rates of reaction without needing to increase temperature, which reduces energy costs

26
Q

Describe one example of a catalyst

A

Enzymes act as catalysts in biological systems

27
Q

What are reversible reactions?

A

Reversible reactions are reactions where the products of the reaction can react to produce the original reactants

28
Q

Define forward reaction

A

When the reactants react together to produce products

29
Q

Define reverse reaction

A

When the products react together to produce the original reactants

30
Q

How do we know if a reaction is reversible?

A

Because of the split arrow symbol

31
Q

How can we change the direction of reversible reactions?

A

The direction of reversible reactions can be changed by changing the reaction conditions (e.g. temperature, concentration, pressure)

e.g:

32
Q

If a reversible reaction is exothermic in one direction, it is ____________ in the opposite direction

A

If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction

heat means endothermic because you are heating it for it to take energy in

33
Q

What happens to the amount of energy transferred in a reversible (exothermic/endothermic) reaction?

A
  • The same amount of energy is transferred in reversible (exothermic/endothermic) reactions as energy cannot be created or destroyed
  • So the amount of energy transferred to the surroundings in one direction of a reversible reaction must be the same as the amount of energy back in when the reaction is in the opposite direction
34
Q

What happens in an equilibrium?

A

In an equilibrium:
- The rate of forward reaction is equal to the rate of the reverse reaction
- There is no overall change in the amounts of products and reactants

Like running up an escalator in the opposite direction

35
Q

Where can equilibrium be reached?

A

Equilibrium can be reached when a reversible reaction occurs in a closed system that prevents the escape of reactants and products

36
Q

Show how equilibrium takes place

A
  • Initially, there are large amounts of reactants and no amounts of products
  • The rate of forward reaction would be really fast as the reaction has just started
  • As the reactants react to form products, the rate of the forward reaction would slow down as there are fewer reactant molecules reacting
  • Meanwhile, the reverse reaction would speed up as the amounts of products gradually increase
  • While the rate of forward reaction slows down and the rate of reverse reaction speeds up, their rates eventually meet and they react at an equal rate

Slow reaction becomes faster, fast reaction becomes slower - until they meet at a point and even out

37
Q

Equilibrium graph

A
38
Q

How can we change the relative amounts of all the reactants and products at equilibrium?

A

We can change the relative amounts of all the reactants and products at equilibrium by changing the conditions of the reaction

39
Q

What does Le Chatelier’s Principle state?

A

If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract and oppose the change, until equilibrium is reached again

oppose - it will do the complete opposite

https://www.youtube.com/watch?v=IYyoncESnmQ

40
Q

What happens if the concentration of a reactant is increased during equilibrium?

A

(Remember, we need to counteract/oppose the original change - so if the concentration increases, we need to find a way to decrease it)

  • If the concentration of a reactant is increased, the rate of forward reaction increases
  • This means more reactants are being used up and products are being formed formed until equilibrium is reached again
41
Q

What happens if the concentration of a product is decreased during equilibrium?

A

If the concentration of a product is decreased, more reactants will react until equilibrium is reached again

42
Q

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

A
  • The relative amount of products at equilibrium increases for an endothermic reaction
  • The relative amount of products at equilibrium decreases for an exothermic reaction
43
Q

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

A
  • The relative amount of products at equilibrium decreases for an endothermic reaction
  • The relative amount of products at equilibrium increases for an exothermic reaction
44
Q

What happens if there is an increase in pressure for a system at equillibrium?

A

An increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction

45
Q

What happens if there is an decrease in pressure for a system at equillibrium?

A

An decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules as shown by the symbol equation for that reaction

46
Q

Describe the effect of a catalyst for a reaction at equillibrium?

A
  • The rates of forward and reverse reaction increase equally, so there is no effect on the rate of reaction
  • So the equillibrium position stays the same
  • However equillibrium is reached more quickly

chemistry (10 decks)

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