C6- The rate and extent of chemical change

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40 Terms

1

What is the rate of a chemical reaction?

How fast the reactants are changed into products

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2

How can you find the speed of a reaction?

-record the amount of product formed over time

-record the amount of reactant used up over time

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3

What do steeper graphs of rate of reaction represent?

faster rates of reaction

<p>faster rates of reaction</p>
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4

How is a finished reaction presented on a rate of reaction graph?

with a straight line (reactants are used up)

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5

What does the rate of a chemical reaction depend on?

-the collision frequency of the reacting particles (more collisions=faster reaction)

-the energy transferred during a collision

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6

What is the activation energy?

the minimum amount of energy needed for the particles to react (used for breaking bonds

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7

What are the 4 things the rate of reaction depends on?

-temperature

-concentration of a solution/pressure of the gas

-surface area

-the presence/absence of a catalyst

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8

What happens when the temperature is increased?

-the particles move faster

-they collide more frequently (so more succesful collisions)

-the faster they move the more energy they have, so more collisions have enough activation energy

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9

What happens when you increase the concentration/pressure?

-collisions between particles are more frequent (less space)

-leads to more succesful collisions

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10

What happens when you increase the surface area?

-for the same volume of a solid, the particles around it have more area to work on

-leads to more collisions (+more succesful collisions)

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11

What happens when you introduce a catalyst?

-decrease the activation energy needed for the reaction

-provide an alternative reaction pathway with a lower activation energy

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12

What is a catalyst?

-speeds up a reaction

-isn't used up

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13

What are enzymes?

biological catalysts

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14

How do you calculate rate of reaction?

knowt flashcard image
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15

How can you measure a reaction with changing turbidity?

-observe a mark through the solution

-measure how long it takes for it to disappear from vision

(although subjective-people don't agree when the mark disappears)

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16

What is turbidity?

cloudiness

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17

What are three ways of measuring rate of reaction?

-percipitation/colour change

-change in mass

-the volume of gas given off

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18

How do you measure ROR with change in mass?

-usually gas given off

-quicker the reading on the balance drops, faster the reaction

-most accurate of the 3 methods

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19

How do you measure ROR with the volume of gas given off?

-use a gas syringe

-the more gas given off during a certain time interval, the faster the reaction

-fairly accurate

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20

What do magnesium and hydrochloric acid react to produce?

hydrogen gas

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21

How can you investigate the effect of concentration on the rate of reaction with Mg and HCl?

-add a set volume of dilute HCl to a connicle flask and carefully place on a mass balance

-add some magnesium ribbon to the acid and quickly plug the flask with cotton wool

-start the stop watch and record the mass on the balance at regular intervals

-plot the results in a table and work out the mass lost for each reading

-plot a graph of time and loss of mass

-repeat with more concentrated acid solutions (keep other variables the same)

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22

How can you investigate the effect of concentration on the rate of reaction with sodium thiosulphate and HCl?

-add a set volume of dilute sodium thiosulphate to a conicle flask

-place the flask on a piece of paper with a black cross drawn on it

-Add dilute HCl to the flask and start the stopwatch

-time how long it takes to go cloudy.

-repeat the reaction with solutions of either reactant at different concentrations (only 1 at a time) (other variables kept the same)

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23

What do sodium thiosulphate and HCl react to produce?

a cloudy yellow percipitate of sulphur

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24

How do you find the mean rate of reaction?

overall change in y value (where the line goes flat) DIVIDED BY total time

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25

How do you find the rate of reaction at a certain point?

-draw a tangent on the point you are investigating

-pick 2 point that are easy to read

-calculate the gradient with change in y DIVIDED BY change in x

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26

What happens in a reversible reaction when the reactants react?

-reactants concentrations falls

-so forward reaction slows down

-but more and more products are formed

-so the products concentration rises

-and the backwards reaction speed up

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27

What will eventually happen in a reverisble reaction?

-the forward reaction will go at the exact same rate as the backwards one

-so the system is at equilibrium

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28

What happens when a system reaches equilibrium?

-both reactions are still happening

-but there is no overall effect (it's a dynamic equilibrium)

-the concentration of reactant and products have reached a balance and won't change

-only occurs in a closed system

-does NOT mean the amounts of reactants/products are equal

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29

What is a closed system?

none of the reactants/products can escape and nothing else can get in

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30

What is the concentration if the equilibrium lies to the right?

the concentration of products is greater than the reactants

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31

What is the concentration if the equilibrium lies to the left?

the concentration of the reactants is greater than the products

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32

What does the position of equilibrium depend on?

-the temperature

-the pressure (only in gases)

-the concentrations

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33

What is an example of a reversible reaction?

hydrated copper sulphate ⇌ anhydrous copper sulphate+ water

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34

What is Le Chatelier's principle?

-the idea that if you change the condition of a reversible reaction at equilibrium, the system will try to counteract that change

-it can be used to predict the effect of any changes you make to a reaction system

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35

LE CHATELIERS PRINCIPLE what happens if you decrease the temperature?

-the equilibrium will move in the exothermic direction to produce more heat

-you will get more products for the exothermic reaction

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36

LE CHATELIERS PRINCIPLE what happens if you increase the temperature?

-the equilibrium will move in the endothermic direction to try to decrease the heat

-you will get more products for the endothermic reaction

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37

LE CHATELIERS PRINCIPLE what happens if you increase the pressure?

If it is a gas:

-the equilibrium tries to reduce it

-moves in the direction with fewer molecules of gas

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38

LE CHATELIERS PRINCIPLE what happens if you decrease the pressure?

It it is a gas:

-the equilibrium tries to increase it

-moves in the direction with more molecules of gas

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39

LE CHATELIERS PRINCIPLE what happens if you increase the concentration of the reactants?

tries to decrease it by making more products

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40

LE CHATELIERS PRINCIPLE what happens if you decrease the concentration of the reactants?

tries to increase it by making more reactants

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