Question

Warm air is heavier than cold air. State whether the above statements is true or false and explain.
(A) True, because warm air contains more heat.
(B) True because warm air molecules are separated by greater distances
(C) False because molecules of warm air expand and become less dense.
(D) False because cold air contains extra temperature than hot air.

Answer 1

Hint: Air has density and volume. Volume of a gas is inversely proportional to density. Warm air molecules have more heat energy, as molecules have more energy there is an increase in distance between molecules. As distance between molecules increases, density decreases.

Complete solution step by step:
- Air is a mixture of different gases. Air present in Earth’s atmosphere has 78 percent of nitrogen and 21 percent of oxygen. It also has carbon dioxide, hydrogen and neon.
- When air is heated or gets heated up, air molecules have high energy and molecules of air start moving which results in increase in distance between air molecules.
- Density of gas is ratio of mass of gas by volume of gas.
- Density is inversely proportional to volume for a given mass. As there is an increase in distance between air molecules, air expands, there is an increase in volume of gas and decrease in density. Less dense air floats over more dense air So Warm air is lighter than cold air.so Warm air is heavier than cold air statement is (C) False because molecules of warm air expand and become less dense.

Note: For constant mass, density of a gas is inversely proportional to volume of gas. As distance between molecules increases, volume also increases as gas molecules occupy more volume and density decreases. For example, when a balloon filled with air is heated up, it starts floating. Warm air is lighter than cold air.