Final answer:
To find the heat released by burning 20.5 g of ethane, convert mass to moles using molar mass, then use the given ΔH for 2 moles of ethane to find the corresponding heat for 0.6833 moles. The calculation reveals that 1055.135 kJ of heat is released.
Step-by-step explanation:
When a 20.5 g sample of ethane, C₂H₆, is burned in an excess of oxygen, the heat released can be calculated using the stoichiometry of the combustion reaction provided and the given enthalpy change (ΔH). The balanced chemical equation for the combustion is 2 C₂H₆ (g) + 7O₂(g) → 4CO₂(g) + 6 H₂O (l) with a ΔH of -3119.4 kJ per 2 moles of ethane combusted.
To find the heat released by the burning of 20.5 g of ethane, we first convert grams to moles using the molar mass of ethane (30.0 g/mol):
20.5 g C₂H₆ * (1 mol C₂H₆ / 30.0 g C₂H₆) = 0.6833 mol C₂H₆
Since the ΔH given is for 2 moles of C₂H₆, we need to calculate the heat released for 0.6833 mol:
(0.6833 mol C₂H₆) * (-3119.4 kJ / 2 mol C₂H₆) = -1055.135 kJ
This means that when 20.5 g of ethane burns, 1055.135 kJ of heat is released.