The Rate And Extent Of Chemical Change

Question 1

What is the rate of reaction?

Answer 1

How fast the reactants are changed into products.

Question 2

What is an example of a slow reaction?

Answer 2

Rusting

Question 3

What is an example of a medium reaction?

Answer 3

Magnesium reacting with acid

Question 4

What is an example of a fast reaction?

Answer 4

Explosions

Question 5

When do chemical reactions occur?

Answer 5

When particles of reactants collide with enough energy to react.

Question 6

What is the energy required for a successful reaction called?

Answer 6

The activation energy

Question 7

What is the activation energy (Ea)?

Answer 7

The minimum amount of energy that particles must have in order to react.

Question 8

What is collision theory?

Answer 8

During any reaction, the reactants must bump into each other in order to react and make a product. These bumps are called collisions. Either the reactants can collide and just bump into each other, or, if they bump with enough energy a product is formed.

Question 9

What factors affect the rate of reaction?

Answer 9

Temperature
Concentration (solutions)/ pressure (gases)
Surface area
Catalysts

Question 10

How does an increase in temperature increase the rate of reaction?

Answer 10

When the temperature is increased, the particles move faster. If they’re moving faster, they’re going more frequently. The faster they move, the more energy they have so more of the collisions will have enough energy to make the reaction happen.

Question 11

How does an increase in concentration/ pressure increase the rate of reaction?

Answer 11

If a solution is more concentrated, it means there are more particles knocking about in the same volume of water (or another solvent). When pressure of a gas increases, the same number of particles occupied a smaller space. This makes collisions between reactant particles more frequent.

Question 12

How does an increase in surface area increase the rate of reaction?

Answer 12

If one of the reactants is a solid, then breaking them up into smaller pieces will increase its surface area to volume ratio. This means that for the same volume of the solid, the particles around it will have more area to work on- so they’re be more frequent collisions.

Question 13

How do catalysts affect the rate of reaction?

Answer 13

A catalyst is a substance that speeds up a reaction without being used up in the reaction itself. This means its not part of the overall reaction equation. Different catalysts are needed for different reactions, but they all work by decreasing the activation energy needed for the reaction to occur. They do this by providing an alternative reaction pathway with a lower activation energy.

Question 14

How can the rate of reaction be observed?

Answer 14

By how quickly the reactants are used up or how quickly the products are formed.

Question 15

How do you calculate the mean rate of reaction?

Answer 15

Amount of reactant used or product formed/ time

Question 16

If the product or reactant is a gas what do you measure it in?

Answer 16

Cm3 and if the time is in seconds cm3/s.

Question 17

If the product or reactant is a solid what do you measure it in?

Answer 17

g

Mol/s

Question 18

What are the 3 ways of measuring the rate of reaction?

Answer 18

Precipitation and colour change.
Change in mass.
Volume of gas given off.

Question 19

What can you use to see a visual change in a reaction?

Answer 19

The initial solution is transparent and the reactant is a precipitate which clouds in water.

Question 20

How do you observe the rate of a reaction?

Answer 20

You can observe a mark through the solution and measure how long it takes for it to disappear, the faster the mark disappears, the quicker the reaction.
Tip- if products are coloured and the reactants are colourless (or vice versa) you can time how long it takes for the solution to lose (or gain) its colour.

Question 21

How do you measure the rate of reaction by observing a change in mass?

Answer 21

As gas is released, the mass disappearing is measured on a balance, the quicker the reading on the balance drops, the faster the reaction

Question 22

How do you measure the rate of reaction by a volume of gas given off?

Answer 22

Involves a gas syringe, more gas given off at a time interval, the faster the reaction.

Question 23

What is the method for the rate experiment for the reaction of magnesium and HCL to produce H2 gas?

Answer 23

1) Add a set volume of dilute hydrochloric acid to a conical flask.
2) Add some magnesium ribbon the the acid and quickly attach an empty gas syringe to the flask.
3) Start the stopwatch and take the readings of the volume of gas in the gas syringe at regular intervals.

Question 24

What is the method for the rate experiment for the effect of using different acid concentration?

Answer 24

Repeat the experiment for the magnesium and HCL one with a number of different concentrations of acid.

Question 25

What is the method for the rate experiment for sodium Thiosulfate and HCL producing a cloudy precipitate?

Answer 25

1) Add a set volume of dilute sodium thiosulfate to a conical flask. 2) Place the flask on a piece of paper with a black cross drawn on it. 3) Add some dilute HCL to the flask and start the stopwatch. 4) Watch the black cross disappear.

Question 26

What is the method for the rate experiment for how the concentration of acid affects the rate?

Answer 26

1) the reaction can be repeated with solutions of either reactant at different concentrations. 2) These results show the effect of increasing the concentration of HCL in the rate of reaction, when added to an excess of sodium Thiosulfate. 3) higher the concentration, the quicker the reaction.

Question 27

How do you find the mean rate of reaction from a graph?

Answer 27

Change in y/ change in x

Question 28

How do you draw a tangent?

Answer 28

1) position a ruler at where you want to find the rate. 2) Adjust the ruler until the space between the ruler and the curved is equal in both sides of the point. 3) Draw along the rule to make the tangent. 4) pick two points in the line that is easy to read, use them to find the gradient of the tangent.

Question 29

What happens in terms of concentration as reactants react?

Answer 29

The forward one will slow down.

Question 30

What happens when more concentration is added to the reaction?

Answer 30

The backward reaction will speed up.

Question 31

What happens to a reaction after a while?

Answer 31

The forward and backward reaction will he going at exactly the same rate- they are at equilibrium.

Question 32

What does it mean that the reactions are at dynamic equilibrium?

Answer 32

Both reactions are happening but there’s no overall effect.

Question 33

What do the circumstances have to be for a reaction to get to dynamic equilibrium?

Answer 33

If the reversible reaction takes place in a closed system- nothing can escape/ get in.

Question 34

Are the amounts of products and reactants equal when the reaction’s at equilibrium?

Answer 34

No

Question 35

If the equilibrium lies to the right...

Answer 35

The concentration of the products is greater.

Question 36

If the equilibrium lies to the left...

Answer 36

The concentration of the reactants is greater.

Question 37

If the reaction is exothermic in one way...

Answer 37

It will be endothermic in the other way. The energy transferred from the surroundings is equal to the energy transferred to the surroundings.

Question 38

What is an example of a reversible reaction?

Answer 38

If you heat blue hydrated copper (ll) solfataras crystals, it drives the water off and leaves white anhydrous copper (ll) sulfur powder- endothermic. If you add some water it turns to the blue crystals again- exothermic.

Question 39

What is Le Chatlier’s principle?

Answer 39

That is you change the conditions of a reversible reaction, the system will counteract that change.

Question 40

What can Le Chatlier’s principle be used to predict?

Answer 40

The effect of any changes you make to a reaction system.

Question 41

How does a decrease temperature affect the reversible reaction?

Answer 41

If you decrease the temperature, the equilibrium will move to the exothermic direction to produce more heat. You’ll get more products for the exothermic and less for the endothermic.

Question 42

How does an increase in temperature affect the reversible reaction?

Answer 42

The equilibrium will move to the endothermic direction and try to decrease it. More products for endothermic and less for exothermic.

Question 43

How does an increase in pressure affect the reversible reaction?

Answer 43

The equilibrium tries to decrease it, moves to a direction where there are fewer molecules of gas.

Question 44

How does a decrease in pressure affect a reversible reaction?

Answer 44

The equilibrium tries to increase it, moves to a direction where there are more molecules of gas.

Question 45

What happens if you increase the concentration of a reversible reaction?

Answer 45

The system tries to reduce it by making more products.

Question 46

What happens if you decrease the concentration of a reversible reaction?

Answer 46

The system tries to increase by reducing the amounts of reactants.

Question 47

What happens if you change the concentration for reactants or products?

Answer 47

System will no longer be at equilibrium.