Question

A mixture of three gasses (H2, Br2 and Cl2) has a total pressure of 73.2 atm. The pressure of Br2 is 9.0 atm and the pressure of Cl2 is 682.5 InHg. If the volume of the gas is 24.0 L and the temperature is 264.7 K, How many moles of H2 are present?(29.9 InHg = 1 atm)

Answer 1

1) List the known and unknown quantities.

Total pressure: 73.2 atm.

Volume: 24.0 L.

Temperature: 264.7 K.

Partial pressures

Sample: Br2

Pressure: 9.0 atm.

Sample: Cl2.

Pressure: 682.5 InHg

Sample: H2.

Pressure: unknown.

2) Partial pressure of H2.

2.1- List the known and unknown quantities.

Partial pressures

Sample: Br2

Pressure: 9.0 atm.

Sample: Cl2.

Pressure: 682.5 InHg

Sample: H2.

Pressure: unknown.

2.2- Set the equation.

Dalton's law. This law states that the total pressure of a gas is equal to the sum of the individual partial pressures.

`P_T=P_(H_2)+P_(Br_2)+P_(Cl_2)`

2.2.1. Convert InHg to atm.

29.9 InHg = 1 atm

`atm=682.5\text{ }InHg*\frac{1\text{ }atm}{29.9\text{ }InHg}=22.83\text{ }atm`

2.3- Plug in the known values and solve for P(H2).

`73.2\text{ }atm=P_(H_2)+9.0\text{ }atm+22.83\text{ }atm`

.

`P_(H_2)=73.2\text{ }atm-9.0\text{ }atm-22.83\text{ }atm`
`P_(H_2)=41.37\text{ }atm`

3) Moles of H2

3.1- List the known and unknown quantities.

Pressure: 41.37 atm.

Volume: 24.0 L.

Temperature: 264.7 K.

Pressure: 41.37 atm

Ideal gas constant: 0.082057 L * atm * K^(-1) * mol^(-1)

3.2- Set the equation.

`PV=nRT`

3.3- Plug in the known quantities and solve for n (moles).

`(41.37\text{ }atm)(24.0\text{ }L)=(n)(0.082057\text{ }L*atm*K^(-1)*mol^(-1))(264.7\text{ }K)`

`n=\frac{(41.37\text{ }atm)(24.0\text{ }L)}{(0.082057\text{ }L*atm*K^(-1)*mol^(-1))(264.7\text{ }K)}`
`n=45.7\text{ }mol`

There are 45.7 moles of H2.

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