To identify a diatomic gas (x2), a researcher carried out the following experiment: she weighed
an empty 3.1-l bulb, then filled it with the gas at 1.00 atm and 28.0 °c and weighed it again.
the difference in mass was 3.5 g. identify the gas.

Aluminium

Explanation:

Given data:

Volume = 3.1 L

Pressure = 1.0 atm

Temperature = 28.0 °C (28 + 273.15 = 301.15 K)

Mass = 3.5 g

Identify the gas.

Solution:

First of all we will find the number of moles.

PV = nRT

n = PV/RT

n = 1 atm × 3.1 L / 0.0821 L. atm. K⁻¹.mol⁻¹× 301.15 K

n = 3.1 L. atm / 24.72 L. atm. mol⁻¹

n = 0.13 mol

Now we will find the molar mass.

molar mass = 3.5 g / 0.13 mol

molar mass = 26.9 g/mol

The gas is diatomic so, atomic mass will be half of 26.9 g/mol.

26.9 g/mol / 2 = 13.45 g/mol

The element which has atomic mass closer to the 13.45 is aluminium.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.