Lec08 Thermochemistry2

# Lec08 Thermochemistry2 - CALORIMETRY A coffee-cup...

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LMLaput Chemistry 16 Lecture 8 CALORIMETRY •A coffee-cup calorimeter is used to measure the amount of heat produced (or absorbed) in a reaction at constant P •If an exothermic reaction is performed in a calorimeter, the heat evolved by the reaction is determined from the temperature rise of the solution. Heat rxn = Heat calorimeter + Heat sol •Amount of heat gained by calorimeter is called the heat capacity of the calorimeter or calorimeter constant . •The value of the calorimeter constant is determined by adding a specific amount of heat to calorimeter and measuring the temperature rise. When 3.425 kJ of heat is added to a calorimeter containing 50.00 g of water the temperature rises from 24.00oC to 36.54oC. Calculate the heat capacity of the calorimeter in J/°C. The specific heat of water is 4.184 J/g°C. 1. Find the temperature change. ΔT = (36.54 – 24.00)°C = 12.54°C 2. Find the heat absorbed by the water in going from 24.00°C to 36.54°C Qp=mCΔT =(50.00g)(4.184 J/g°C)(12.54°C) =2623.37 J ≈ 26.23J 3. Find the heat absorbed by the calorimeter take the total amount of heat added to calorimeter and subtract the heat absorbed by the water. 3.425 kJ = 3425 J (3425 J – 2623 J) = 802 J 4 Find the heat capacity of the calorimeter. (heat absorbed by the calorimeter) / (ΔT) ±²³´ µ²¶·¸³ ± ¹ º »¼¶½¾¾ ¿ ± À Á »Â¶Ã ¿ ± À . A coffee-cup calorimeter is used to determine the heat of reaction for the acid-base neutralization CH 3 COOH (aq) + NaOH (aq) NaCH 3 COO (aq) + H 2 O (l) When we add 25.00 mL of 0.500 M NaOH at 23.000°C to 25.00 mL of 0.600 M CH 3 COOH already in the calorimeter at the same temperature, the resulting temperature is observed to be 25.947°C. The heat capacity of the calorimeter has previously been determined to be 27.8 J/°C. Assume that the specific heat of the mixture is the same as that of water, 4.18 J/g°C and that the density of the mixture is 1.02 g/mL.

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Lec08 Thermochemistry2 - CALORIMETRY A coffee-cup...

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