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
To find the total energy needed to break the bonds, we use the bond energies provided:
For 2 mol of H–H bonds:
Energy = 2 × 435 kJ mol⁻¹ = 870 kJ
For 1 mol of O=O bond:
Energy = 1 × 500 kJ mol⁻¹ = 500 kJ
Thus, the total energy needed to break the bonds is:
extTotalEnergy(break)=870+500=1370extkJ
Step 2
Calculate the energy released when bonds are formed
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Answer
When products are formed, bonds are created. The energy released during bond formation is calculated as follows:
For 4 O–H bonds in 2 mol of water, (since each water molecule contains 2 O–H bonds):
Energy = 4 × 460 kJ mol⁻¹ = 1840 kJ
Thus, the energy released when bonds are formed is:
extTotalEnergy(release)=1840extkJ
Step 3
Calculate the energy change
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Answer
The energy change (ΔH) for the reaction is calculated using the formula:
