A pair of studnets performed an experiment to determine the heat of formation of

Question

A pair of studnets performed an experiment to determine the heat of formation of zinc oxide. The reastions are entirely analogous to the reactions of megnesium and magnesium oxide you did in the lab. They reacted 1.504g zinc with 100.20g of 0.05M hydrochloric acid. (Zinc of the limiting reagent.) The inital temperture was 23.11 degrees C and the final temperture was 31.36 degrees C. If the heat capacity of the zinc chloride solution formed in this reaction is 4.06Jg-1 degrees C-1 and the calorimeter constant is 27J degrees C-1, calculate the quantity of heat energy acquired by the surroundings in this experiment. Be sure you follow sig figs in your answer.

Explanation / Answer

mass of the solution = mass of HCl+ mass of Zinc= 100.2+1.504=101.704 gm

specific heat of solution = 4.06, temperature change= 31.36-23.11= 8.25 deg.c

hence heat given to the solution = mass of solution* specific heat* temperature difference= 101.704*4.06*8.25=3407 joules

heat taken by calorimeter= heat capacity of calorimeter* temperature difference= 27*8.25 =223 joules

total heat taken by surrousinfdings= 3407+223= 3630 joules, since Zinc is the limiting reactant, moles of Zinc= mass/atomic weight =1.504/65.38 =0.023 moles

since heat is liberated, the reaction is exothermic.

hence enthalpy change=- 3630/0.023 J/mole =-157799 J/mole

this much heat is given to surroundings.

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