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gcse chemistry > c8 - rates and equilibrium > Flashcards

c8 - rates and equilibrium Flashcards

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1
Q

define rate of reaction

A

speed of a reaction

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2
Q

how can you work out rate of a chemical reaction?

A
  • find out how quickly reactants are used up as they make products
  • find out how quickly the products of the reaction are made
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3
Q

how can you find out how quickly reactants are used up in some reactions?

A

by measuring the mass of the reactant mixture
- if reaction gives off a gas, then mass of mixture decreases

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4
Q

how can gradient of a graph help us work out rate of reaction?

A

the steeper the gradient, the faster the reaction is at that time

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5
Q

how can a graph for rate of reaction be produced?

A

by measuring the mass of gas released or volume of gas produced at intervals of time

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6
Q

give the two possible equations for mean rate of reaction after a given time.

A

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

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7
Q

define collision theory

A

states that reactions only happen if particles collide

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8
Q

define activation energy

A

minimum energy particles need to react

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9
Q

give two ways of increasing rate of reaction

A

1) increasing frequency of reacting particles colliding with eachother
2) increase the energy they have when they collide

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10
Q

what happens when you increase frequency of collisions or energy of particles?

A

rate of reaction will increase

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11
Q

give factors for increasing rate of reaction

A
  • increasing temperature
  • increase concentration of reactants in solids
  • increase pressure of reacting gases
  • increase surface area of solids
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12
Q

how can rate of reaction be increased through surface area?

A

1) breaking large solids into smaller pieces exposes more surface area
2) this leads to more collisions and so a powder reacts faster than large lumps
3) finer the powder, faster the reaction

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13
Q

why do powders react faster than large pieces of solid?

A

more surface area

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14
Q

what happens to rate of reaction when temperatures increase?

A

increases
- because particles collide more often
- particles collide with more energy

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15
Q

what happens to particles when there is a rise of 10 degrees from room temperature/

A

rate of reactions is doubled, so particles collide twice as fast

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16
Q

what must you remember when talking about particles in an exam?

A

don’t say ‘more collisions’ instead say ‘more frequent collisions’ or ‘collisions occur more often’

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17
Q

what happens to rate of reaction when you increase the concentration?

A
  • increases rate of reaction because there are more particles of the reactants moving around in the same volume of solution.
  • increased frequency of collisions results in a faster reaction
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18
Q

what happens to rate of reactions when pressure is increased?

A
  • increased pressure squashes gas particles more closely together
  • more particles of a gas in a given space
  • produces more frequent collisions so increases rate of reaction
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19
Q

how can you find rate of reaction?

A
  • by plotting volume of gas given off as reaction progresses over time
  • see how long it takes to collect a fixed volume of gas using same apparatus
20
Q

define a catalyst

A
  • changes rate of reaction
  • not used up or changed chemically in reaction so can be reused
21
Q

how do catalysts increase rate of reaction?

A
  • provide an alternative reaction pathway to the products with a lower activation energy
  • higher proportion of the reactant particles have sufficient energy to react
  • frequency of effective collisions increases
22
Q

what benefits does using catalysts in industrial processes have?

A
  • they can reduce energy and time needed for reactions
  • this reduces cost and reduces impact on environment
23
Q

define reversible reactions

A

when products react together to make original reactants again

24
Q

how are reversible reactions presented?

A

2 ‘half arrows’ are used
- one point forward, one points backwards

25
Q

what happens when ammonium chloride is heated?

A

decomposes to produce ammonia gas and hydrogen chloride gas

26
Q

what happens when ammonia gas and hydrogen chloride gas cool down?

A

they react to form ammonium chloride again

27
Q

in reversible reactions, the forwards and reverse reactions involve…

A

equal but opposite energy tranfers

28
Q

amount of energy released by the exothermic reaction…

A

exactly equals the amount taken in by the endothermic reaction

29
Q

if a reversibe reaction is exothermic in one directions…

A

must be endothermic in the other

30
Q

what happens when you heat blue hydrated copper (II) sulfate crystals

A

an endothermic reaction (exothermic reverse)

31
Q

what happens when water is added to anhydrous copper (II) sulfate?

A

hydrated copper (II) sulfate is formed
- exothermic reaction in this direction

32
Q

define anhydrous

A

substance that doesn’t contain water

33
Q

why must blue copper (II) sulfate be heated continuously to change it into anhydrous copper (II) sulfate?

A

the water is driven off, producing anhydrous copper sulfate which is a white solid
- endothermic reaction

34
Q

what does blue hydrated copper (II) mean?

A

copper and sulfate ions in its crystal structure are surrounded by water molecules

35
Q

why does adding water to anhydrous copper (II) sulfate cause mixture to get hot?

A
  • Hydrogen bonding occurs between the solute and the solvent, releasing energy
  • exothermic reactions
36
Q

define closed system

A

no reactants or products can escape

37
Q

what happens in a reversible reaction when rate of forward reaction equals rate of backwards reaction?

A

equilibrium is reached

38
Q

define equilibrium

A

both reactions continue to happen, but amount of reactants and products remain constant

39
Q

how can you change relative amounts of reactants and products in a reacting mixture at equlibrium?

A

change conditions
- this is important for chemical industry in controlling reactions

40
Q

define le chatelier’s principle

A

when a change in conditions is introduced to a system at equilibrium, the positiion of equilibrium shifts as to cancel out the change

41
Q

what happens if you increase concentration of a reaction

A

will cause more products to be formed as system tries to achieve equilibrium

42
Q

what happens if you remove a product?

A

more reactants will try and achieve equilibrium so more product is formed

43
Q

what happens if the forward reaction produces more molecules of gas?

A
  • an increase in pressure decreases amount of products formed
  • decrease in pressure increases amount of products formed
44
Q

what happens if forward reaction produces fewer molecules of gas?

A
  • an increase in pressure increases amount of products formed
  • decrease in pressure decreases amount of products formed
45
Q

what happens if forward reaction is exothermic?

A
  • increase in temperature decreases amount of products formed
  • decrease in temperature increases amount of products formed
46
Q

what happens if forward reaction is endothermic?

A
  • increase in temperature increases amount of products formed
  • decrease in temperature decreases amount of products formed
47
Q

why would rate decrease during a reaction?

A
  • particles being used up
  • less chance of collision

gcse chemistry (10 decks)

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