Question

Part A) A sample of a gas at 25°C and 1.0 atm pressure has a volume of 2.5 L. The container is allowed to expand until the pressure is 0.85 atm and the temperature is 15°C. The final volume of the gas is __________ L.

Part B) A reaction is carried out that produces hydrogen gas. The gas is collected in an inverted beaker over water at 25 ^oC. The vapor pressure of water at 25 ^oC is 23.78 mmHg. The total pressure in the beaker is determined to be 755.3 torr. What is the partial pressure (in units of torr) of the hydrogen gas in the beaker?

Part C) CH₃SH gas and NH₃ gas both have strong distinctive odors. If containers of each of these two gases are opened at the front of a room at the same time, which one will be smelled first by the people sitting in back of the room?

A.		CH3SH
B.		NH3
C.		Since they are ate the same temperature they will both diffuse at the same rate so will be smelled at the same time.
D.		Neither will diffuse to the back of the room so they will not be smelled by the people in the back of the room.

Answer 1

Part A

assuming the gas behaves as an ideal gas, we use the following equation
PV = nRT
The moles (n) are preserved in state 1 and state 2, being a closed container.
Hence n2 = n1

State 2: ------> (i)

State 1: ------> (ii)

equalize (i) with (ii), and we solve for V2

  simplifying R   

P1=1atm; V1=2.5L T1=25+273=298 K (must be in absolute temperatureit must be in absolute temperature)

P2=0.85atm ; T2=15+273=288K

   

Part B

According to Dalton's Law

Partial pressure of H2 = total pressure - vapor pressure of water
1 torr=1mmHg

total pressure=755.3 torr; vapor pressure of water=23.78mmHg=23.78torr

Partial pressure of H2 =755.3 torr - 23.78torr

Partial pressure of H2 =731.52 torr

Part C

Graham's law sets out that the rate of effusion of a gas is inversely proportional to the square root of the mass of its particles. This formula can be written as:

where:

Rate1 is the rate of effusion of the first gas (volume or number of moles per unit time).
Rate2 is the rate of effusion for the second gas.
M1 is the molar mass of gas 1
M2 is the molar mass of gas 2.

If gas 1= NH3 and gas 2= CH3SH so   

Where

M(CH3SH)=48.10g/mol

M(NH3)=17.03g/mol

   ----------->

The diffusion rate of NH3 is 1.7 greater than the rate of CH3SH
Therefore the answer is B (NH3)