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Help me understand this GCSE past paper question?

Hi there,

I'm going over some past papers as part of my revision for my Core Science GCSEs, but I have no clue what to do for a lot of the questions on the June 2013 Unit 2 Higher Chemistry paper; even after looking at the mark scheme I'm still totally confused. Could someone briefly explain to me what the answers are to this question and why, or tell me which area I need to revise to understand this? Thank you!

This is the questions I'm struggling with:

Sodium hydrogencarbonate is used as baking powder for making cakes. When the cake mixture is baked the sodium hydrogencarbonate decomposes.
The equation for the reaction is: 2 NaHCO3(s) --Heat--> Na2CO3(s) + H2O(g) + CO2(g)

1 (b) (i) The cake mixture rises when baked. Use the equation to suggest why. (1 mark)

1 (b) (ii) The same reaction can be reversed to produce sodium hydrogencarbonate from sodium carbonate.
Na2CO3 + H2O + CO2 ---> 2 NaHCO3
Do the reactants need to be heated? Give a reason for your answer. (1 mark)
Reply 1
the mixture expands (rises) because of the gases made

is the reaction forward exo or endothermic, what will the reverse be
Reply 2
1 - carbon dioxide is produced, it is a gas and so gets trapped in the mixture and causes cake to rise

2 - yes, to break the bonds in the reactants, providing enough energy to reach activation enthalpy so initiate the reaction.
Reply 3
No, the reactants need not to be heated because the reaction is exothermic.

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