The Rate and Extent of Chemical Change

Question 1

What are the four factors affecting rate of reaction?

Answer 1

Temperature, Surface area, Concentration/Pressure, Catalyst

Question 2

How does the temperature increase the rate?

Answer 2

• temperature increase particles move faster
• move faster = more frequent collisions
• move faster = gain energy, more collisions have enough energy to make reaction happen

Question 3

How does the concentration or pressure increase the rate?

Answer 3

• more concentrated = more particles colliding much more frequently in the same volume
• pressure increased = same number of particles occupies smaller space, collisions more frequent

Question 4

How does the surface area increase the rate?

Answer 4

solid = breaking it up into smaller pieces will increase SA:V

same volume of solid -> the particles around it have more area to work on so there will be more frequent collisions

Question 5

How does a Catalyst increase the rate and what is a Catalyst?

Answer 5

Catalyst = substance that speeds up the rate of reaction by decreasing the activation energy without being used up. They provide an alternative reaction pathway.

Question 6

Equation for the rate of reaction ?

Answer 6

amount of reactants used or product formed/ time

Question 7

What would the units be for the rate of reaction?

Answer 7

cm3/s
g/s
mol/s

Question 8

How could you investigate the colour change?

Answer 8

• initial solution transparent, product precipitate which clouds the solution.
• observe mark and measure how long it takes to disappear
• reactants coloured, product colourless = time how long it takes for the solution to lose or gain its colour

Question 9

How would you investigate the change in mass?

Answer 9

• speed of reaction that produces gas = mass balance
• gas released mass disappears
• quicker reading drops faster the reaction
• regular intervals = plot reaction graph
• most accurate way

Question 10

How would you investigate the volume of gas given off?

Answer 10

• gas syringe measures volume of gas given off
• more gas given off during given time = faster reaction
• quite accurate, give to the nearest cm3, measurements at regular intervals and plot graph
• if the reaction is too vigorous the plunger may easily be blown off

Question 11

What is crude oil?

Answer 11

Crude oil is a mixture of hydrocarbons formed from the remains of simple marine organisms over millions of years.

Question 12

What are the uses of crude oil?

Answer 12

cars, trains, planes. Diesel oil, kerosene, heavy fuel

Question 13

How does the petrochemical industry use crude oil?

Answer 13

uses some of the hydrocarbons from the cruse oil as a feedstock to make new compounds for things like polymers, solvents and lubricants

Question 14

What is the homologous series?

Answer 14

carbon atoms bonded together to form different groups. These groups contain similar compounds with many properties in common. E.g Alkenes and alkanes

Question 15

How are short-chain hydrocarbons different from long-chain ones?

Answer 15

Short-chain = flammable, make good fuels
long-chain = thick gloppy liquids that aren't at all useful

Question 16

What is cracking?

Answer 16

The splitting up of long-chain Hydrocarbons to form short-chain hydrocarbons.
Alkane molecules turned into smaller, more useful ones.
Alkanes are produced by cracking as well.

Question 17

How does Cracking happen?

Answer 17

• thermal decomposition - breaking molecules down by heating them
• heat long-chain to vaporise them
• vapour passed over hot powdered aluminium oxide catalyst
• long-chain split apart on the surface of the specks of catalyst - catalytic cracking

Question 18

What is another way of cracking hydrocarbons?

Answer 18

Vaporise them, mix with steam and then heat to very high temperature. Steam cracking.

Question 19

Describe Fractional Distillation

Answer 19

• oil heated until most is gas. gas enters fractionating column - liquid drained off
• column = temperature gradient, hot at bottom and gets cooler as you go up
• longer hydrocarbons = higher boiling point. Condense back into liquid and drain out of the column early on when at bottom.
• shorter hydrocarbons = lower boiling point. Condense and drain out later on, near top
• crude oil separated out into different fractions. each fraction similar number of carbon atoms = similar boiling point of hydrocarbons