A Short Blog About the Quality of Short Written Responses.

A chemistry GCSE question

CO(g) + 2 H2 ⇌ CH3OH(g) 

The reaction is carried out at a temperature of 250oC and a pressure of 100 atmospheres. 

The forward reaction is exothermic. 

Explain what happens to the yield of methanol if a temperature higher than 250oC is used.

[2 marks}

AQA June 2018

An answer you might be pleased to see:

The yield of methanol would decrease because a higher temperature favours the endothermic reaction, which is forwards.

The following would probably also get 2 marks:

This is a reversible reaction so the production of carbon monoxide and hydrogen is endothermic, meaning there will be more energy for this reaction to take place, so less CH3OH will be made since the CO and H2 will have a higher yield so there will be less methanol. 

Science GCSE encourages ‘good enough’ answers. Time spent developing the quality of written explanation beyond a certain point does not translate into better exam performance. 

This could be addressed using comparative judgement. If all of the answers were compared and judged and given a scaled score from 0 to 2, you could reward clarity of explanation. It would be worth spending time teaching a skill which is meaningful and important – the ability to communicate scientific concepts accurately and succinctly. 

If GCSEs become obsolete and we are given control of our curriculum, this gets my vote.



  1. Hi Roger,
    I share your desire to teach learners of science to aspire to increasing levels of precision and accuracy in their spoke and written work.
    To this end I have been developing an AI that reads short answer responses in science and provides detailed feedback.
    One beauty of such a tool is that a traditional two mark question can be marked with a depth simply not possible by people and mark every answer consistently.
    I just wanted to reach out in case it was something you were interested in for research or for other purposes.


    1. Hi Mark – this is something a friend and I have unsuccessfully played with over the last few years. I’d be really interested in discussing. Ben


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s