How many moles of gas X are present if the gas has a volume of 2dm³ at room temperature and pressure? Give your answer to 2 decimal places.

Approximately , assuming that this gas is an ideal gas.

Explanation:

Look up the standard room temperature and pressure: and .

The question states that the volume of this gas is .

Convert the unit of all three measures to standard units:

.

.

.

Look up the ideal gas constant in the corresponding units: .

Let denote the number of moles of this gas in that . By the ideal gas law, if this gas is an ideal gas, then the following equation would hold:

.

Rearrange this equation and solve for :

.

In other words, there is approximately of this gas in that .

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.