Question

Part A) Two identical pieces of machinery are lifted from the sidewalk to the roof of a 100.0 m tall building. One is lifted directly to the building's roof and has a change in internal energy of 1059 kJ. The other is lifted to twice the height of the building and then lowered to the roof. What is the change in internal energy of the second piece of machinery once it has reached the roof?

Part B) Indicate the sign of the enthalpy change, ΔH, in the following process carried out under atmospheric pressure, and indicate whether the process is endothermic or exothermic:

An "Instant Cold" pack is squeezed and shaken, mixing and activating the combination of chemicals inside the pack.

ΔH is _____ and the process is _____

Part C) When 50.0 mL of 0.100 M AgNO3 and 50.0 mL of 0.100 M HCl are mixed in a constant-pressure calorimeter, the temperature of the mixture increases from 22.30 °C to 23.11 °C. The temperature increase is caused by the following reaction:.

AgNO₃(aq) + HCl(aq) → AgCl(s) + HNO₃(aq)

Calculate ΔH for this reaction in kJ/mol AgNO₃, assuming that the combined solution has a mass of 100.0 g and a specific heat of 4.18 J/g °C.

Answer 1

1. Internal energy is state function and is independent of path. Hence change in internal energy remains same at 1059 Kj

2. The delH is +Ve and the process is endothermic ( Reaction between ammonium nitrate and water)

3. Mass of the solution = 100gm specific heat= 4.18 J/g.deg.c and temperature rise= 23.11-22.3=0.81 deg.c

Enthalpy change = mass* specific heat* temperature difference= 100*4.18*0.81=338.58 joules

Moles of AgNO3 used= Volume* Molarity= (50/1000)*0.1 =0.005 moles

0.005 moles of AgNO3 gives rise to 338.58 joules

Enthakoy for the reaction = 338.58/0.005 J/mol=67716 Joules/mole =67.716 Kj/mol