Question

THERMOCHEMISTRY Calculating molar heat capacity A chemist carefully measures the amount of heat needed to raise the temperature of a 762.0 mg sample of CHF, from 0.8 °C to 14.2 "C. The experiment shows that 14.8 J of heat are needed. What can the chemist report for the molar heat capacity of CHF,? Round your answer to 3 significant digits. mol. x ? Explanation Check

Answer 1

If (Cm) is the molar heat capacity, (n) is the number of moles of the substance, (AT) is the temperature change, then the quantity of heat absorbed or released (Q) can be calculated using the relation: Q=nxCm XAT According to the question, Mass, m = 762 mg 1g = 762 mg * 1000 pag (1 g = 1000 mg) = 0.762 g The molar mass of CHF, is 114.092 g.mol-1 Therefore, the number of moles is calculated as follows: Mass Number of moles =- Molar mass 0.762 g 114.092 g.mol-1 = 6.68x10- mol The amount of heat needed, Q=14.8 J Temperature difference, AT = (14.2 – 0.8)°C = 13.4°C = 13.4K The temperature difference remains same for both °C and kelvin Substitute the values in equation (1) to calculate the molar heat capacity as follows: Q=nxCm X AT 14.8 J=6.68x10-3 mol x Cm 13.4 K 14.8 J m 6.68x10- mol x13.4 K = 165.34 J.mol-1. K-1 Hence, the value of molar heat capacity is 165.34 J·moll.K-1.