At 11:30 pm at a large university on a night during finals week, 7500 students each use an electrical heater to heat 450 g of water from 20°C to 100°C to make a cup of coffee. How many kJ of electrical energy is consumed to make their beverages? Assume 100% efficiency.(C = 75.291 J/mol . K for H₂O; q = C_cal$\Delta$T)

Question

Quizplus · Accepted Answer

To calculate the energy consumed, use q = mCΔT. Convert 450 g of water to moles (450 g / 18 g/mol = 25 mol). Then, q = 25 mol * 75.291 J/mol·K * (100°C - 20°C) = 15058.2 J per student. For 7500 students, total energy = 15058.2 J * 7500 = 1.129365 x 10^8 J = 1.1 x 10^5 kJ.

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