Chapter 14.2, Problem 4RQ

Interpretation Introduction

Interpretation: The reason methane to be a gas and water to be a liquid under normal conditions is to be given despite of both having similar molar masses.

Concept introduction: For compounds with similar molar masses, under normal conditions their physical state depends on the intermolecular forces.

Answer to Problem 4RQ

Under normal conditions, water is a liquid and methane is a gas because of the presence of hydrogen bonding in water which is absent in case of methane.

Explanation of Solution

For compounds with similar molar masses, under normal conditions their physical state depends on the intermolecular forces. The intermolecular forces are the forces that bind the molecules together. In methane only weak London dispersion forces are present whereas in water along with London dispersion forces, hydrogen bonding is also present. It is due to the presence of strong hydrogen bonding in water that water molecules are held tighter to each other resulting in its existence as a liquid and not a gas like in case of methane.

Conclusion

Under normal conditions, water is a liquid and methane is a gas because of the presence of hydrogen bonding in water which is absent in case of methane.