Measuring energy changes questions

Assignment: Measuring energy changes short answer questions

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When 100 cm3 of 1.00 mol dm−3 sodium hydroxide solution, NaOH(aq), is added to 100 cm3 of 1.00 mol dm−3 hydrochloric acid, HCl(aq), the temperature increases from 19.3 oC to 26.1 oC.

Determine the enthalpy change of neutralization for the reaction.

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A student determined the enthalpy change for the reaction:

CuSO4(aq) + Zn(s) → Cu(s) + ZnSO4(aq)

She placed 50 cm3 of 0.140 mol dm−3 copper sulfate solution in a polystyrene cup and recorded the temperature for two minutes before adding an excess of zinc powder. She continued stirring and taking the temperature for a further fifteen minutes to produce the following graph.

 

i. Determine the temperature increase if there had been no heat lost to the surroundings and hence the enthalpy change for the reaction.

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ii. State two assumptions that have been made in order to calculate the answer above from the data given.

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1.21 g of ethanol, C2H5OH, was burned in a spirit burner. The heat produced raised the temperature of 400 g of water placed in a beaker above the flame from 17.0 oC to 29.9 oC.

i. Calculate the enthalpy change, in kJ mol−1, for the reaction taking place.

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ii. State four reasons why this value is not equal to the data book value for the standard enthalpy of combustion of ethanol, which is given as – 1371 kJ mol−1.

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Consider the following enthalpy level diagram:

i. What process is occurring during this reaction?

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ii. Distinguish between energy and enthalpy.

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iii. Explain whether the products are more or less thermodynamically stable than the reactants.

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