||What causes the Greenhouse Effect?
In this activity, students check and clarify their understanding of the greenhouse effect. They work independently before collaborating with a partner to compare and evaluate their ideas and agree a joint view. This view is then compared with the ideas of other pairs of students.
This activity is best used to consolidate and to check on learning after students have spent some time on this topic.
- understand the cause of the greenhouse effect.
Sequence of activities
Demonstrate the greenhouse effect using Classic chemistry demonstrations 68, emphasising the observed temperature changes but without providing an explanation at this stage. Invite students to say what phenomenon is illustrated by the demonstration and then share the learning objective with them.
Hand out a copy of the Student sheet to each student.
Ask them to draw, by themselves, an annotated diagram to explain the greenhouse effect.
Divide students into pairs. Ask them to
- compare their diagrams
- justify their ideas, where there are differences
- agree a common diagram which they draw on an OHT or produce a PowerPoint slide.
Bring together students in a plenary. Ask:
- one group to show and explain their diagram to the class using an OHP or a data projector
- other groups to add to it (from their own diagram) until all key points have been described.
Remind students of the demonstration used to start the session.
Question them on what the lamp and lead foil represented (Sun and Earth).
Ensure that students modify their original diagram, where necessary, to take account of what other students have said during the session.
||Take in the student diagrams and write comments which reinforce the good features. Identify any points that still need developing and indicate where additional support can be found.
Assessment for learning commentary
The demonstration is a key part of the session and a key to its objective.
The process of comparing diagrams draws students into assessing themselves and their fellow students. It encourages them to listen to the ideas of others.
In the plenary, the students experience a wider range of ideas. They then reassess the completeness of their original diagram.
Even though this may be a final session on this topic, written feedback remains important. It confirms achievement or guides students on how to clarify their understanding.
For each student
For demonstration 68 from Classic chemistry demonstrations
- One 275 W photoflood light bulb and a suitable plain bulb holder (ie one without a shade)
- Two identical 250 cm3 beakers
- Two mercury in glass thermometers (0‑100 °C)
- Two discs of lead foil cut to fit the bases of the beakers
- A source of carbon dioxide gas.
Expected explanation of the greenhouse effect
- Visible radiation is emitted from the hot sun.
- Some of this radiation is absorbed by the Earth which is consequently warmed.
- Warm earth emits infrared radiation.
- Some of the radiation is absorbed by greenhouse gases such as carbon dioxide. Carbon-oxygen bonds in carbon dioxide molecules vibrate more vigorously.
- Molecules excited in this way collide with other molecules in the atmosphere and spread absorbed energy around.
- The atmosphere becomes warmer.
It is the responsibility of the teacher to carry out an appropriate risk assessment.
T. Lister, Classic chemistry demonstrations. London: Royal Society of Chemistry, 1995.