Hydrogen burns in air at a temperature well above 100°C to form water. (i) The boiling points of hydrogen and water are shown in Figure 15. Use this information to add the missing state symbols to the equation for the reaction taking place as the hydrogen burns. 2H₂(____) + O₂(g) → 2H₂O(____) (ii) The atom economy for the reaction in (i) is 100%. State how the equation shows that the atom economy is 100%. (b) Lead can be obtained by heating its oxide with carbon. The balanced equation for the reaction is: 2PbO + C → 2Pb + CO₂ Calculate the atom economy for the production of lead in this reaction. (relative atomic masses: C = 12, O = 16, Pb = 207; relative formula masses: PbO = 223, CO₂ = 44) Give your answer to two significant figures.

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Hydrogen burns in air at a temperature well above 100°C to form water - Edexcel - GCSE Chemistry - Question 10 - 2018 - Paper 1

Question 10

Hydrogen burns in air at a temperature well above 100°C to form water. (i) The boiling points of hydrogen and water are shown in Figure 15. Use this information to... show full transcript

Worked Solution & Example Answer:Hydrogen burns in air at a temperature well above 100°C to form water - Edexcel - GCSE Chemistry - Question 10 - 2018 - Paper 1

Step 1

2H₂() + O₂(g) → 2H₂O()

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Answer

The missing state symbols for the equation are:

For hydrogen (H₂), it is a gas under standard conditions, so the symbol is (g).
For water (H₂O), since it is formed at a temperature above 100°C, it is in gaseous state as well, thus the symbol is also (g).

The complete balanced equation is:

$2H₂(g) + O₂(g) → 2H₂O(g)$

Step 2

State how the equation shows that the atom economy is 100%.

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Answer

The atom economy is calculated by comparing the total mass of the desired product to the total mass of all reactants. In this case, all atoms from the reactants are accounted for in the product water (2H₂O).

As there are no by-products formed in the reaction, it shows that:

$\text{Atom Economy} = \frac{\text{Mass of useful products}}{\text{Total mass of reactants}} \times 100 = 100\%$

Step 3

Calculate the atom economy for the production of lead in this reaction.

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101 rated

Answer

To calculate the atom economy:

Determine the relative formula mass of the reactants and useful product:
- Total mass of reactants = 2 × (223) + 12 = 458
- Mass of useful product (lead) = 2 × (207) = 414
Calculate the atom economy using the formula:

$\text{Atom Economy} = \frac{\text{Mass of useful products}}{\text{Total mass of reactants}} \times 100$

Substituting the values:

$\text{Atom Economy} = \frac{414}{458} \times 100 = 90.39\%$

After rounding to two significant figures, the answer is 90%.

Hydrogen burns in air at a temperature well above 100°C to form water - Edexcel - GCSE Chemistry - Question 10 - 2018 - Paper 1

Worked Solution & Example Answer:Hydrogen burns in air at a temperature well above 100°C to form water - Edexcel - GCSE Chemistry - Question 10 - 2018 - Paper 1

2H₂(____) + O₂(g) → 2H₂O(____)

State how the equation shows that the atom economy is 100%.

Calculate the atom economy for the production of lead in this reaction.

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2H₂() + O₂(g) → 2H₂O()