Chemistry - Thermochemistry Question with Solution | TestHub
In certain areas where coal is cheap, artificial gas is produced for house hold use by the 'water gas' reaction:
C(s) + H2O(g) → H2(g) + CO(g)
Assume that coke is 100% carbon. Given ΔHC (kcal/mol) at 25°C: H2(g) = -68.0; CO(g) = -68.0; C(s) = -94.0. Select the correct option(s): (one or more than one correct)
Options:(select one or more)
Answer:
Solution:
First, calculate the moles of carbon (C) in 1.2 kg of coke.
Given that 1.2 kg of coke is equivalent to 1200 g, and the molar mass of carbon is approximately 12 g/mol:
nC = 1200 g/(12 g/mol) = 100 mol C
(a) If 100 mol of carbon is completely burned, the heat produced is 100 × 94 = 9400 kcal. This statement is true.
(b) When each mole of carbon reacts to produce water gas, it yields 1 mol of H₂ and 1 mol of CO. The combustion of these products gives:
1 mol H₂ + 1 mol CO tarrow 68 kcal + 68 kcal = 136 kcal.
Therefore, 100 mol of carbon reacting this way would produce 100 × 136 = 13,600 kcal. This statement is true.
(c) One mole of carbon reacting to form water gas produces 30 g of water gas (2 g H₂ + 28 g CO).
If 1200 g of coke is used, this corresponds to 40 mol C-equivalents for water gas production (since 1200 g / 30 g/mol = 40 mol).
The heat produced would be 40 × 136 = 5440 kcal. This statement is true.
(d) The statement that 13,600 kcal is the same as 9400 kcal for the same mass of coke is false, as these are different values.
The correct answers are (a), (b), and (c).
