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 hydrogen gas, H₂, with 1 mol of oxygen gas, O₂, to give 2 mol of steam, H₂O. Figure 14 | bond | bond energy in kJ mol⁻¹ | |------|-------------------------| | H – H | 435 | | O – O | 500 | | O – H | 460 | energy change = ___________________________ kJ mol⁻¹

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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 energy required to break the bonds in the reactants:

There are 2 H–H bonds and 1 O=O bond being broken:

$ext{Energy needed to break bonds} = (2 imes 435) + (1 imes 500) = 870 + 500 = 1370 ext{ kJ mol}^{-1}$

Step 2

Calculate the energy released when bonds are formed

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Answer

Next, we determine the energy released when 4 O–H bonds are formed (as there are 2 H₂O molecules produced):

$ext{Energy released when bonds are formed} = 4 imes 460 = 1840 ext{ kJ mol}^{-1}$

Step 3

Calculate the energy change

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Answer

Finally, we can find the energy change for the overall reaction:

$ext{Energy change} = ext{Energy required to break bonds} - ext{Energy released when bonds are formed}$

Thus:

$ext{Energy change} = 1370 - 1840 = -470 ext{ kJ mol}^{-1}$

This indicates that the reaction is exothermic, releasing energy.

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