Chemistry ✿ the rate and extent of chemical change

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24 Terms

1

equation for mean rate of reaction

total amount of products/ reactants (g or cm³) / time taken (s)

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2

dm³ → cm³

multiply by 1000

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3

what 4 conditions can increase the rate of reaction?

how does higher temperatures increase the rate?

  • increase surface area

  • high temperature

  • high concentration

  • high pressure

more kinetic energy causes more successful collisions

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4

why do smaller objects such as powders increase the rate of reaction?

  • have a larger surface area to volume ratio,

  • so more collisions of particles take place

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5

collision theory

chemical reactions can only occur when particles collide with enough energy

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6

activation energy

the minimum amount of energy used by particles so they react

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7

catalyst

substances which increase rate of chemical reaction by providing an alternative reaction pathway with a lower activation energy

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8

how can the student investigate how the rate of reaction when the concentration of is changed by measuring the volume of gas produced?

  • use 50cm³ of 1mol/dm³ hydrochloric acid

  • use 3cm magnesium ribbon

  • set up a conical flask containing 50cm³ of 1mol/dm³ hydrochloric acid

  • have bung and delivery tube attached to gas syringe prepared

  • add a 3cm piece of magnesium ribbon

  • quickly fit bung on conical flask and start a stopwatch

  • record the measurement of gas produced every 10 seconds

  • repeat experiment with 2 and 3 mol/dm³ hydrochloric acid

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9

how can the student investigate how the rate of reaction when the concentration of is changed by observing change of colour or turbidity?

  • use 10cm³ sodium thiosulfate solution

  • use 10cm³ dilute hydrochloric acid

  • pour 10cm³ of sodium thiosulfate solution into a conical flask

  • measure out 40cm³ water with a measuring cylinder and pour into conical flask

  • add 10cm³ dilute hydrochloric acid into conical flask and place it on a black cross and start a stopwatch

  • record the time it takes for the cross to disappear

  • repeat using other concentrations of sodium thiosulfate

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10

reversible reaction

a reaction were the products can also form the reactants. If one direction is exothermic, the other one is always endothermic

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11

exothermic

transfers energy to the surroundings

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12

endothermic

takes in energy from surrounding

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13

equilibrium

when the forward and backward reaction in a reversible reaction happen at the same rate in a sealed container

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14

le chatelier’s principle

when a change of conditions happens to a system at equilibrium, the position of equilibrium moves to cancel out the change

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15

If the concentration of a system at equilibrium is increased, what happens to the equilibrium?

  • equilibrium shifts to opposite side of substance which has increased concentration

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16

If the concentration of a system at equilibrium is decreased, what happens to the equilibrium?

  • equilibrium shifts to the side of substance which has decreased concentration

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17

(for gaseous reactions)
If the pressure of a system at equilibrium is increased, what happens to the equilibrium?

  • the equilibrium position will shift towards the side with the smaller number of molecules

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18

(for gaseous reactions)

If the pressure of a system at equilibrium is decreased, what happens to the equilibrium?

  • the equilibrium position will shift towards the side with the larger number of molecules

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19

If the temperature of a system at equilibrium is increased, what happens to the equilibrium?

  • equilibrium shifts to the endothermic side to increase products

  • the products at the exothermic side decrease

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20

If the temperature of a system at equilibrium is decreased, what happens to the equilibrium?

  • equilibrium shifts to the exothermic side to decrease products

  • the products at the endothermic side increase

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21
<p>The equilibrium mixture is <strong>cooled. </strong></p><p>Explain what happens to <u>the concentration</u> of the <strong>pink cobalt compound. [3]</strong></p>

The equilibrium mixture is cooled.

Explain what happens to the concentration of the pink cobalt compound. [3]

  • concentration increases

  • because equilibrium moves to the left

  • because the reverse reaction is exothermic

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22

Suggest why a catalyst is used in this industrial process.

Do not give answers in terms of increasing the rate of reaction. [1]

lowers energy costs

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23

Suggest the effect of using the catalyst on the equilibrium yield of methanol. [1]

catalysts don’t effect the yield

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24

what is meant by a closed system?

a system where the reactants or products cannot escape or enter

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