How many grams of butane must be burnt to heat 10 kg of water from 30°C to 100°C? (Heat of combustion of butane is −700 kcal/mol and specific heat of water is 1 cal g⁻¹ K⁻¹).
Correct answer: A. 58 gm
- A. 58 gm
- B. 56 g
- C. 54 g
- D. 52 g
Explanation
First, calculate the heat required to warm the water: Q = mcΔT = (10,000 g)(1 cal/g°C)(70°C) = 700,000 cal = 700 kcal. Since the combustion provides 700 kcal/mol, exactly 1 mole of butane is needed. The mass of 1 mole of butane (C₄H₁₀) is 58 g.
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Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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