This question is about oxygen. Hydrogen reacts with oxygen. $$2 H_2 (g) + O_2 (g) \rightarrow 2 H_2O (g)$$ Figure 2 shows the relative energies of the reactants and products at a certain temperature. Label the activation energy on Figure 2. [1 mark] Determine the overall energy change for the reaction between hydrogen and oxygen shown in Question 03.1 Use Figure 2. [2 marks] Oxygen is in Group 6 of the periodic table. Figure 3 shows the outer energy levels in one molecule of oxygen (O₂). Draw the electrons in the outer energy levels in Figure 3. [2 marks] The equation shows the decomposition of hydrogen peroxide. $$2 H_2O_2 \rightarrow 2 H_2O + O=O$$ Table 1 shows the bond energies. Calculate the overall energy change for the reaction. [3 marks]

GCSE AQA Chemistry Combined Science Measurement, Mass & Equations: This question is about oxygen.

This question is about oxygen - AQA - GCSE Chemistry Combined Science - Question 3 - 2019 - Paper 1

Question 3

This question is about oxygen. Hydrogen reacts with oxygen. $$2 H_2 (g) + O_2 (g) \rightarrow 2 H_2O (g)$$ Figure 2 shows the relative energies of the reactants a... show full transcript

Worked Solution & Example Answer:This question is about oxygen - AQA - GCSE Chemistry Combined Science - Question 3 - 2019 - Paper 1

Step 1

Label the activation energy on Figure 2.

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Answer

The activation energy can be labeled by drawing a line from the reactants at approximately 800 kJ up to the peak of the curve, which reaches around 2160 kJ.

Step 2

Determine the overall energy change for the reaction between hydrogen and oxygen shown in Question 03.1.

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Answer

To determine the overall energy change, subtract the energy of the products from the energy of the reactants. From Figure 2, the energy of the reactants (H2 and O2) is 800 kJ and the energy of the products (H2O) is 300 kJ. Therefore, the overall energy change is:

$\text{Energy change} = E_{reactants} - E_{products} = 800 \text{ kJ} - 300 \text{ kJ} = 500 \text{ kJ}$

Step 3

Draw the electrons in the outer energy levels in Figure 3.

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In Figure 3, each oxygen atom will have six electrons in its outer level. These can be represented as dots, with two shared pairs of electrons (indicating the bond) overlapping between the two oxygen atoms.

Step 4

Calculate the overall energy change for the reaction.

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Answer

To calculate the overall energy change for the decomposition of hydrogen peroxide:

Bonds broken:
- Energy for two O-O bonds: 2 × 138 kJ = 276 kJ
- Energy for two O-H bonds: 4 × 463 kJ = 1852 kJ
Total for bonds broken:

$\text{Total energy (bonds broken)} = 276 + 1852 = 2128 \text{ kJ}$
Bonds formed:
- Energy for two O-H bonds: 2 × 496 kJ = 992 kJ
Total for bonds formed:

$\text{Total energy (bonds formed)} = 992 \text{ kJ}$
Energy change calculation:
- Energy change = Bonds broken - Bonds formed:
$\text{Energy change} = 2128 \text{ kJ} - 992 \text{ kJ} = 1136 \text{ kJ}$

This question is about oxygen - AQA - GCSE Chemistry Combined Science - Question 3 - 2019 - Paper 1

Worked Solution & Example Answer:This question is about oxygen - AQA - GCSE Chemistry Combined Science - Question 3 - 2019 - Paper 1

Label the activation energy on Figure 2.

Determine the overall energy change for the reaction between hydrogen and oxygen shown in Question 03.1.

Draw the electrons in the outer energy levels in Figure 3.

Calculate the overall energy change for the reaction.

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