a chemical reaction occurs in 75.00 mL of aqueous solution, releasing a gas. The
ID: 476216 • Letter: A
Question
a chemical reaction occurs in 75.00 mL of aqueous solution, releasing a gas. The gas collected has a volume of 473 mL of gas at 22 degrees Celsius on a day when the atmospheric pressure was 757 torr. The reaction caused the solution to cool from 22.0 degrees Celsius to 19.5 degrees Celsius. Assume that the volume of the solution does not change and that the solution is essentially water (Specific heat is 4.184 J/g-K and density is 1.00g/mL). Will the work be + or -. Will q for the solution be + or -. Calculate the work in Joules. Calculate the heat transferred in Joules and the change in energy in Joules.
Explanation / Answer
The reaction forms a gas with the following properties
Volume = 473mL = 0.473 L
Temperature = 22 degree C = 22 + 273.15 K = 295.15 K
pressure = 757 Torr = 0.99 atm
Moles of gas formed = PV / RT
R = gas constant = 0.0821 L atm / mole K
Moles = 0.99 X 0.473 / 0.0821 x 295.5 = 0.0193 moles
the difference in temperature = 22 - 19.5 = 2.5
The gas expands so there is work done by the system = Positive
work done = Pressure (V2-V1) = 0.99 (473-75) = 394.02 L atm = 39 922.05 joules
Q = Mass of water X specific heat of water (change in temperature)
Mass of water = Volume X density = 75 X 1 = 75 grams
Q = 75 X (4.184) ( 19.5- 22) = -784.5 Joules
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