Hydrogen reacts with oxygen to form steam - Edexcel - GCSE Chemistry - Question 10 - 2018 - Paper 1
Question 10
Hydrogen reacts with oxygen to form steam.
2H₂(g) + O₂(g) → 2H₂O(g)
Bond energies are shown in Figure 14.
Calculate the energy change for the reaction of 2 mol of... show full transcript
Worked Solution & Example Answer:Hydrogen reacts with oxygen to form steam - Edexcel - GCSE Chemistry - Question 10 - 2018 - Paper 1
Step 1
Calculate the energy needed to break bonds
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Answer
The energy needed to break the bonds is calculated as follows:
For 2 moles of H–H bonds:
2×435=870 kJ
For 1 mole of O=O bonds:
1×500=500 kJ
Thus, the total energy needed to break the bonds is:
870+500=1370 kJ
Step 2
Calculate the energy released when bonds are formed
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Answer
The energy released when bonds are formed is calculated as follows:
For the formation of 2 moles of O–H bonds:
2×460=920 kJ
Thus, the total energy released when the bonds are formed is:
1840 kJ
Step 3
Calculate the overall energy change
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Answer
The overall energy change (ΔE) can be calculated by subtracting the energy needed to break bonds from the energy released when bonds are formed:
ΔE=Energy released−Energy needed
In this case:
ΔE=1840−1370=470 kJ
Since the reaction is exothermic, the energy change can also be reported as 'energy released'.
