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5 (a) Balance the chemical equation for the combustion of methane - AQA - GCSE Chemistry - Question 5 - 2016 - Paper 3
Question 5
5 (a) Balance the chemical equation for the combustion of methane. $$CH_4 + O_2 \rightarrow CO_2 + H_2O$$ 5 (b) Alcohols are used as fuels. A group of students in... show full transcript
Worked Solution & Example Answer:5 (a) Balance the chemical equation for the combustion of methane - AQA - GCSE Chemistry - Question 5 - 2016 - Paper 3
Step 1
Step 2
Calculate the heat energy (Q) in joules, released by burning 0.8 g of the alcohol.
Answer
We can calculate the heat energy using the following values:
- Mass of water (m) = 50 g
- Specific heat capacity (c) = 4.2 J/g/°C
- Temperature change (ΔT) = 38.4 °C - 22.0 °C = 16.4 °C
Using the formula:
Substituting the values:
Step 3
Use the bond energies to calculate the overall energy change for this reaction.
Answer
To find the overall energy change, we first need to calculate the total bond energy of bonds broken and formed. For ethanol combustion:
Bonds broken:
- 5 C–H bonds = 5 x 413 kJ/mol = 2065 kJ/mol
- 3 O=O bonds = 3 x 498 kJ/mol = 1494 kJ/mol Total energy of bonds broken = 2065 + 1494 = 3560 kJ/mol
Bonds formed:
- 4 C=O bonds = 4 x 799 kJ/mol = 3196 kJ/mol
- 6 O–H bonds = 6 x 467 kJ/mol = 2802 kJ/mol Total energy of bonds formed = 3196 + 2802 = 5998 kJ/mol
Overall energy change:
Overall energy change = Energy of bonds broken - Energy of bonds formed = 3560 - 5998 = -2438 kJ/mol.
Step 4
Step 5
Complete the energy level diagram for the combustion of ethanol.
Answer
On the energy level diagram, label the following:
- Activation energy: The energy required to initiate the reaction, which is typically the difference in energy from the reactants to the peak of the energy hill.
- Overall energy change: This will be represented as a downward slope from the energy level of reactants to the energy level of products, indicating that energy is released during the reaction.