Page 75 - Science Coursebook

5.2 More exothermic reactions

Questions

1 What are the products when magnesium and hydrochloric acid react?

2 How did Noor and Hanif know when the reaction had finished?
A+I 3 Hanif thought that more heat energy had been given out by his reaction
because in his experiment the end temperature was higher. Noor thought that
both reactions gave out the same amount of heat energy. Whose idea was
correct? Explain why.
SE 4 Explain why it was a good idea to wear safety glasses.
SE 5 Noor and Hanif wondered how they could produce a higher temperature
SE

change. Their ideas included adding more magnesium, using a different metal

and using a different acid.

Write each of these three ideas as a scientific question to be investigated.

Activity 5.2
Planning an investigation into the reaction between acid and magnesium

SE 1 Choose one of the questions from question 5 (or one of your own) and write a
plan for your investigation.
• Before you write your plan, try out the reaction between magnesium and
an acid. In this preliminary work you should practise measuring the
temperature change.
• You also need to find out how big a change in the variable (for example, the

length of magnesium ribbon) is needed to make a change in temperature
that you can measure.
• When the reaction takes place and heat energy spreads out into the
environment, are you sure that you are accurately measuring the
temperature change? What could you do to reduce this heat loss?
• Decide on how you will record and present your results.
2 Ask your teacher to check your plan.
3 Carry out your plan. You may find that you want to make changes to it once

you begin doing the experiment. If so, write down the changes that you have
made, and explain why you made them.

Questions
A1 What can you conclude from your results?
A2 Compare your results with others in the class. Are your results in agreement
with others who carried out the same investigation?
A3 How could you improve your investigation?

Summary
• When metals react with water or acids, heat energy is given out.
• The reaction of a metal with water or with an acid is exothermic.

5 Energy changes 73