A calorimeter has a heat capacity of 40.00 kJ/ oC (note this unit is different). Complete combustion of 1.00 g of H2 in this calorimeter causes a temperature increase of 3.54 oC. Calculate the molar enthalpy of combustion (∆Hcomb) from this evidence. ∆H system = ±|q surroundings| n ∆H combustion = mc∆T (0.5 mol) ∆H comb = (40.00 kJ/ oC)(3.54 oC) ∆H comb = 283.2 kJ/mol = 2.83 x 102 kJ/mol What mass of lithium chloride must have dissolved if the temperature of 200.0 g of water increased by 6.0 C? ∆Hsol = -37 kJ/mol for LiCl. ∆H system = ±|q surroundings| n ∆H solution = mc∆T n (37 000 J/mol) = (200.0g)(4.18 J/g· ºC)(6.0 ºC) n = 0.1356 mol Mass of LiCl = n x MM = 0.1356 x 42.5 g/mol = 5.8 g
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