Section 15 and 16

Question 1

Reaction rates

Answer 1

Reaction is a measure of how fast reaction happens
Rate of reaction= amount used ÷ time
Different ways rate of reaction can be measured – precipitation, change in maths (usually gas given off), the volume of gas given off

Question 2

Rate experiments

Answer 2

Increasing surface area temperature pressure and concentration equals a higher rate of reaction and frequency of collisions
Calculating rates – faster rates are shown by steeper gradient – draw a tangent to find gradient of curve – gradient = change in Y ÷ change in X
Finer particles of solid mean a higher rate

Question 3

Collision theory

Answer 3

Particles must collide with enough energy in order to react
Increasing the 10th concentration and surface area increases rate
The more collisions the higher the rate of reaction

Question 4

Catalysts

Answer 4

Enzymes control cell reactions – enzymes are biological catalysts
Catalyst increases the rate of reaction by decreasing the activation energy

Question 5

Endo and Exothermic reactions

Answer 5

Exo = Hot (rise in temp)
Endo = cool (fall in temp)
Activation energy is the energy needed to start a reaction

Question 6

Measuring temperature changes

Answer 6

Changing temp depends on reactant used
Can measure change and temp through – dissolving salts in water(endo), neutralisation reactions, displacement reaction, precipitation reaction (exo for rest)

Question 7

Bond energies

Answer 7

Energy must always be supplied to break bonds
Energy is released when you bonds are formed
Positive energy change = endothermic
Negative energy change = EXothermic
Bond breaking = endothermic
Bond forming = exorhermic

Overall energy change = energy required to break bonds – energy released by forming bonds

Question 8

Fractional distillation

Answer 8

1. oil heated and pumped into bottom of tall tower where it’s vaporises
2. very hot at bottom, cold top as vaporised oil rises, it cools and condenses
3. heavy fractions have a high boiling points and condenser near bottom

It’s the process by which crude oil is separated – gases, petrol, kerosene, diesel oil, fuel oil (going down)
Long chain molecules have stronger intermolecular forces so has a high melting and boiling points (more energy needed to break)

Question 9

Hydrocarbons

Answer 9

Alkanes- saturated hydrocarbon, formula = CnH2n+2 ,colour in bromine water = stays orange

alkenes -unsaturated hydrocarbon, formula = CnH2n, colour in bromine = brown –> colourless

Fuels release energy in combustion reactions
Long chain – low boiling point, volatility = easy, viscosity = runny
Short chain – high boiling points, volatility = hard, viscosity = thick

Question 10

Pollutants

Answer 10

Incomplete combustion produces toxic carbon monoxide and soot
Sulphur dioxide causes acid rain
Oxides of nitrogen are also pollutants
Hydrogen can be used as clean renewable fuel – expensive and hard to store

Question 11

Cracking

Answer 11

Cracking is splitting up long chain hydrocarbons
Involves heat, moderate pressure and a catalyst
Helps match supply and demand

Alkane heated up until it’s vaporised it breaks down when comes in contact with catalyst then creates a mixture of short chain alkane and alkene

Question 12

The atmosphere

Answer 12

Phase 1 – volcanoes gave out Steve and carbon dioxide – this condensed to form oceans
Phase 2 – green plants evolved and produced oxygen through photosynthesis using carbon dioxide
Phase 3 – ozone layer allows evolution of complex animals
Carbon dioxide decreased due to photosynthesis
Water vapour increased due to formation of oceans

Question 13

The greenhouse effect

Answer 13

Greenhouse effect helps keep the Earth warm
1.earth radiates some of the heat radiation it’s absorbs as longer wavelength (infrared radiation)
To.some of the infrared radiation is absorbed by greenhouse gases
3.some infrared radiation is reflected back to earth by greenhouse gases
4.some infrared radiation is readmitted back into space
This keeps Earth warm
Three greenhouse gases – carbon dioxide, water vapour and methane
Human activity affects the composition of air – population increasing, more people respiring giving out more carbon dioxide – deforestation

Question 14

Climate change

Answer 14

Increasing concentration of greenhouse gases reason enhanced greenhouse effect – more heat radiation absorbed – atmosphere heats up(Slow down by reducing the amount of greenhouse gases released)
Historical data is much less accurate than current records – can look at tree rings fossils and gas bubbles
Problems- rising sea levels, drout, desertification, ice caps melting