The Rate And Extent Of Chemical Change

Question 1

How is rate of reaction calculated?

Answer 1

Rate of reaction = amount (e.g. grams) of reactant used or product formed / time

Question 2

What are the various units for rate of reaction?

Answer 2

Mass/time, volume/time, moles/time (can include g/s or cm3 or mol/s)

Question 3

What are the common ways of measuring rate of reaction?

Answer 3

• loss in mass of reactants
• volume of gas produced
• time for a solution to become opaque

Question 4

Describe measuring the rate of reaction by monitoring mass loss

Answer 4

Place the reaction flask on a balance. In these reactions a gas is given off, so record the decrease in mass in time intervals -> plot a graph of mass vs time

Question 5

Describe measuring the rate of reaction by monitoring the volume of a gas

Answer 5

Connect a gas syringe to a reaction flask and measure the volume of a gas formed in time intervals -> plot a graph of volume vs time

Question 6

Describe measuring the rate of reaction by monitoring the disappearance of a cross

Answer 6

Take a piece a paper and mark a cross (X) on it. Put the reaction flask on this cross. Mix the reagents, and measure how long it takes for a cloudy mixture to conceal a cross

Question 7

How do you find a rate of reaction at some time from a graph of the amount of reactant vs time?

Answer 7

• pick a point corresponding to the time and find the tangent to the curve at this point
• the tangent is the gradient of this graph - it tells you how fast the reaction proceeds at this point
• the steeper the tangent line, the faster the rate
• gradient of tangent can be expressed in change in y values over change in x values

Question 8

What five factors affect the rate of a chemical reaction?

Answer 8

• concentration
• pressure of gases
• surface area
• temperature
• catalysts

Question 9

What is activation energy?

Answer 9

the minimum quantity of energy which the reacting species must possess in order to undergo a specified reaction. It is also called sufficient energy

Question 10

How does concentration/pressure affect the chemical reaction?

Answer 10

More particles per unit of volume ~ collision will be more frequent and will increase the rate of reaction

Question 11

How does surface area affect chemical reactions?

Answer 11

The smaller the surface area ~ more frequent the collisions are and will increase the rate of reaction

Question 12

How does temperature affect the chemical reaction?

Answer 12

As the temperature increase, the particle gain more energy ~ move faster, collide more frequently and will increase the rate of reaction (up 20 degrees can double the reactions)

Question 13

How can catalyst affect the chemical reaction?

Answer 13

Higher proportions of catalysts ~ more successful collisions and will increase the rate of reaction

Question 14

What is a catalyst?

Answer 14

Substance that can be used to speed up a reaction without being used up in the reaction themselves

Question 15

What is the collision theory?

Answer 15

Chemical reaction can occur only when the reacting particles collide with each other with sufficient energy (more than or equal to activation energy)

Question 16

What is an enzyme?

Answer 16

Molecule that acts as a catalyst in a biological system

Question 17

What is a reversible reaction?

Answer 17

A reversible reaction occurs when the product of a reaction can react backwards to produce the originals reactants

Question 18

When is dynamic equilibrium reached?

Answer 18

In a closed system, when the forward and reverse reactions occur at the same rate and the concentrations of reactants and products remain constant

Question 19

Describe Le Chatelier’s Principle

Answer 19

If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract change and restore the equilibrium

Question 20

Describe the effect of change the concentration of reactant and product on the position of the equilibrium

Answer 20

If the concentration of one of the reactant or products is changed, the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium us reached again. If concentration of a reactant is increased more products will be formed until equilibrium is reached again. If the concentration of a product is decreased, more reactants will react until equilibrium is reached again

Question 21

Describe the effect of changing temperature on the position of the equilibrium

Answer 21

If the temperature of a system at equilibrium is increased
- the relative amount of products at equilibrium increases for an endothermic reaction
- the relative amount of products at equilibrium decreases for an exothermic reaction

Question 22

Describe the effect of changing pressure (of gases) on the position of the equilibrium

Answer 22

An increase in pressure causes the equilibrium positions to shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction. A decrease in pressure causes the equilibrium position shift towards the side with a larger numbers of molecules as shown by the symbol equation for that reaction. Pressure has no effect on the reactions where the numbers of gas molecules are equal on both sides of the equation

Question 23

Describe the effect of a catalyst on the position of the equilibrium

Answer 23

No effect -> it just speeds up both forward and backward reactions equally i.e. equilibrium is achieved faster

Question 24

What is concentration?

Answer 24

A measurement of how much solute exists within a certain volume of solvent

Question 25

What is gas pressure?

Answer 25

The force that the gas exerts on the walls of its container

Question 26

What is finding the rate?

Answer 26

Amount of reactant used or product formed

Question 27

How do you find the mean rate from reactants?

Answer 27

Reactant used / time

Question 28

How do find the mean rate of products?

Answer 28

Product formed / time

Question 29

What the the rate from a graph?

Answer 29

The steeper the gradient is, the faster the rate

Question 30

What is the mean rate?

Answer 30

Average rate over a time range

Question 31

What is a specific rate?

Answer 31

Reaction rate at a specific time

Question 32

How do you calculate the gradient?

Answer 32

Change in y / change in x