In a calorimetry experiment, 50.0 g of water is heated by 6.0 K by burning 0.025 mol of fuel (c = 4.18 J g-1 K-1). What is the enthalpy of combustion?
Answer and explanation
Correct answer: A. -50.2 kJ mol-1
- Step 1: J. Step 2. Per mole: J mol-1 = 50.2 kJ mol-1. Step 3. The temperature rises, so the reaction is exothermic: negative sign. Answer: -50.2 kJ mol-1. Why not the others: -1.25 kJ mol-1 forgets to divide by the moles; -50.2 J mol-1 omits the conversion to kJ; +50.2 kJ mol-1 gives the wrong sign for an exothermic reaction.
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