Explain why radiation from the Sun passes through the atmosphere but radiation from the Earth's surface largely does not.

Greenhouse gases do not absorb the short wavelength radiation coming in, but they do absorb the longer wavelength infrared going out.

What happens to the energy that a greenhouse gas molecule absorbs?

The molecule re-emits it in all directions, so some of it travels back down to the Earth's surface.

Why is the greenhouse effect necessary for life on Earth?

Without it the energy would escape to space and the Earth's average temperature would be far too cold for life.

OCR GCSE Combined Science Chemistry J250

Chemical Reactions

Topic overview Writing formulae of elements and compounds Balanced equations, and deducing formulae from ions State symbols in equations Conservation of mass, and changes of mass in open systems Exothermic and endothermic reactions, and reaction profiles Activation energy and why reactions need it Oxidation and reduction in terms of oxygen Acids, alkalis and neutralisation The ionic equation for neutralisation, and reactions of acids The pH scale, acidity and alkalinity Measuring pH with indicators and pH meters Products at the electrodes, and molten ionic compounds Electrolysis of aqueous solutions Inert and non-inert electrodes

Elements, Compounds and Mixtures

Topic overview Purity, and melting point data Relative formula mass and empirical formulae Formulations, and separating mixtures Paper and thin layer chromatography Interpreting chromatograms and Rf values Choosing a purification method Metals and non-metals in the Periodic Table Electron arrangement and position in the Periodic Table Ionic, covalent and metallic bonding compared Dot and cross diagrams, and the limits of models Reactions, electron arrangement and Mendeleev's table Carbon's four bonds, and the variety of organic compounds Diamond, graphite, fullerenes and graphene Bond strength, intermolecular forces and predicting state Bulk properties of ionic, molecular and giant structures

Global Challenges

Topic overview Extracting metals by reduction and by electrolysis Life cycle assessment Recycling, and the decisions behind it Fractional distillation of crude oil The fractions, and crude oil as a feedstock Dependence on hydrocarbons, and cracking The Earth's early atmosphere, and how oxygen developed The greenhouse effect, and evidence for climate change Effects of carbon dioxide and methane, and air pollutants Producing potable water

Monitoring and Controlling Chemical Reactions

Topic overview Measuring the rate of a reaction, and rate graphs Factors affecting rate, and collision theory Surface area and rate Catalysts and how they work Reversible reactions and dynamic equilibrium Activation energy, and enzymes as catalysts

Particles

Topic overview The particle model and changes of state How the atomic model changed, and the structure of the atom The size of atoms, and the subatomic particles Calculating protons, neutrons and electrons

Predicting and Identifying Reactions

Topic overview Groups 1, 7 and 0, and why they behave as they do Predicting reactivity from the Periodic Table Reactivity of metals with water and acids Tests for oxygen, hydrogen, carbon dioxide and chlorine

Global Challenges

The greenhouse effect, and evidence for climate change

3 things to know
Paper 4 (Chemistry)

Overview

Three greenhouse gases, how the greenhouse effect traps infrared radiation and why life needs it, the effect of more greenhouse gas, the correlation between fossil fuel use and carbon dioxide, ice core evidence, the uncertainty in the evidence and in climate predictions, judging climate claims, peer review, communicating findings, and the ethics of cutting emissions.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Describe the greenhouse effect.

Key term

Name three greenhouse gases.

Key term

What type of radiation does the Earth's surface emit after it has been warmed?

Questions from this subtopic

Each one with the model answer underneath.

1
Name three greenhouse gases.
Model answer
Carbon dioxide, methane and water vapour.
2
Describe the greenhouse effect.
Model answer
Short wavelength radiation from the Sun passes through the atmosphere and warms the Earth's surface, the surface re-emits energy as longer wavelength infrared radiation, and greenhouse gases absorb this infrared and re-emit some of it back towards the surface.
3
What type of radiation does the Earth's surface emit after it has been warmed?
Model answer
Infrared radiation, of longer wavelength than the radiation it received from the Sun.
4
Explain why radiation from the Sun passes through the atmosphere but radiation from the Earth's surface largely does not.
Model answer
Greenhouse gases do not absorb the short wavelength radiation coming in, but they do absorb the longer wavelength infrared going out.
5
What happens to the energy that a greenhouse gas molecule absorbs?
Model answer
The molecule re-emits it in all directions, so some of it travels back down to the Earth's surface.
6
Why is the greenhouse effect necessary for life on Earth?
Model answer
Without it the energy would escape to space and the Earth's average temperature would be far too cold for life.

See the rest and revise

Other ways to work this

The same content, four other ways.

What is inside Levo

Six ways to work the same material.

1Closed book

2Open book

3Closed book

The 3-step method, run for you

Answer cold, learn it, then prove it stuck. Levo tracks the jump between your first attempt and your last.

Chemical Reactions

Elements, Compounds and Mixtures

Global Challenges

Monitoring and Controlling Chemical Reactions

Cram a whole paper in one sitting

Sort every topic into what you know and what you do not, then drill only the weak ones.

Values 7.

belowaboveat

Blank Blitz makes facts automatic

Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AMetals are on the left and in the centre, and non-metals are on the right-hand side.

BKI, because potassium loses one electron and iodine gains one.

CCaCl₂, because a calcium atom loses two electrons and each chlorine atom gains one.

Build It gets the exam shape right

Assemble a full-mark answer from its marking points, in the order an examiner wants them.

Sodium ions give a bright yellow flame colour.

TrueFalse

Test It catches misconceptions

Spot the fault in a statement. The traps are the mistakes students actually make.

721941163128510

Brain Breaks between sessions

Short focus games to reset attention, so the next set lands better than the last.

Every question in Global Challenges, on a schedule.

Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.

Start revising, £5 a month See how the method works

Or £46 a year, about £3.83 a month. Cancel anytime.