According to the equation C6H6(I) + 15/2 O2(g) ➞ 6CO2(g) + 3H2O(1), H = -3264.4 KJ/mol, the energy evolved when 7.8 g of lizene is burnt in air will be:
Correct answer: C. 326.4 KJ/mol
- A. 163.32 kj/mol
- B. 32.64 kj/mol
- C. 326.4 KJ/mol
- D. 3.264 kJ/mol
Explanation
To calculate the energy evolved when 7.8 g of benzene (C6H6) is burnt in air, we need to use the given enthalpy change (∆H) and the molar mass of benzene. Given data: ∆H = -3264.4 kJ/mol (the negative sign indicates that the reaction is exothermic, meaning energy is released) Molar mass of C6H6 (benzene) = 78.11 g/mol Step 1: Calculate the number of moles of benzene burnt. Number of moles = mass / molar mass Number of moles = 7.8 g / 78.11 g/mol Number of moles ≈ 0.1 mol Step 2: Calculate the energy evolved for 0.1 moles of benzene. Energy evolved = ∆H × number of molesEnergy evolved = -3264.4 kJ/mol × 0.1 mol Energy evolved = -326.44 kJ The energy evolved when 7.8 g of benzene is burnt in air will be approximately 326.44 kJ. The negativesign indicates that energy is released during the combustion process. Option C is correct.
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About Thermochemistry and Energetics of Chemical Reactions
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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