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11 Nov 2019
A typical "instant" cold pack makes use of the endothermic dissolving of NH_4NO_3(s) into water. Use the following formula to calculate the # of grams ofNH_4NO_3 (MW = 80 g/mol) needed to lower the temperature of 500 g of H_2O to 5 degree C. Assume that the initial temperature of the water is 25 degree C (room temperature). Cp (water) = 75 J/mol K (watch your units: KJ/mol and J/mol K!!!). Delta H_rxn = +30 kJ/mol. Delta T = - nsalt(Delta Hrxn)/nwater(Cpwater) Delta T = T_final - T_initial n_salt = # of moles of salt dissolved n_water = # of moles of water used cp = heat capacity of solvent Delta H_rxn = enthalpy of dissolving salt in solution (also called Delta H_sol)
A typical "instant" cold pack makes use of the endothermic dissolving of NH_4NO_3(s) into water. Use the following formula to calculate the # of grams ofNH_4NO_3 (MW = 80 g/mol) needed to lower the temperature of 500 g of H_2O to 5 degree C. Assume that the initial temperature of the water is 25 degree C (room temperature). Cp (water) = 75 J/mol K (watch your units: KJ/mol and J/mol K!!!). Delta H_rxn = +30 kJ/mol. Delta T = - nsalt(Delta Hrxn)/nwater(Cpwater) Delta T = T_final - T_initial n_salt = # of moles of salt dissolved n_water = # of moles of water used cp = heat capacity of solvent Delta H_rxn = enthalpy of dissolving salt in solution (also called Delta H_sol)
Bunny GreenfelderLv2
1 Jan 2019