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Respiration and Air Properties - Condensation and Evaporation in Air

Grade 5CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Respiration is the process where living things take in O2O_2 (Oxygen) and give out CO2CO_2 (Carbon Dioxide), water vapor (H2OH_2O), and energy.

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Exhaled air is generally warmer and contains more moisture (water vapor) than the air we inhale from the surroundings.

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Evaporation is the process by which water changes from a liquid state to a gaseous state (H2O(l)→H2O(g)H_2O_{(l)} \rightarrow H_2O_{(g)}) due to an increase in temperature or heat.

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Condensation is the process where water vapor (gas) changes back into liquid water droplets (H2O(g)→H2O(l)H_2O_{(g)} \rightarrow H_2O_{(l)}) when it comes into contact with a cooler surface or loses heat.

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In the context of breathing, when the warm water vapor in our breath touches a cold surface like a mirror or window pane, it cools down and undergoes condensation, forming tiny droplets of water.

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Humidity refers to the amount of water vapor present in the air. High humidity means the air is holding a lot of H2OH_2O molecules in gaseous form.

📐Formulae

Food(Glucose)+Oxygen→Carbon Dioxide+Water Vapor+EnergyFood (Glucose) + Oxygen \rightarrow Carbon\ Dioxide + Water\ Vapor + Energy

Liquid Water→HeatingWater Vapor (Evaporation)Liquid\ Water \xrightarrow{Heating} Water\ Vapor\ (Evaporation)

Water Vapor→CoolingLiquid Water (Condensation)Water\ Vapor \xrightarrow{Cooling} Liquid\ Water\ (Condensation)

💡Examples

Problem 1:

Why does a mirror become 'foggy' when you blow air onto it from your mouth?

Solution:

The 'fog' is actually formed by the process of condensation.

Explanation:

Our exhaled breath contains warm water vapor (H2O(g)H_2O_{(g)}). When this warm air touches the surface of the mirror, which is at a lower temperature, the vapor loses heat energy. This causes the gaseous water to turn back into tiny liquid droplets (H2O(l)H_2O_{(l)}) that stick to the glass, making it appear foggy.

Problem 2:

During a cold winter morning, why can we see 'smoke-like' clouds coming out of our mouths when we breathe?

Solution:

This is due to the rapid condensation of water vapor in the cold air.

Explanation:

The air inside our lungs is warm and moist. When we exhale, this warm H2OH_2O vapor hits the very cold outside air. The sudden drop in temperature causes the vapor to condense instantly into a tiny mist of liquid water droplets, which we see as a small cloud.

Problem 3:

If a wet cloth is kept in the sun, it dries up. Which process is occurring here?

Solution:

The process is Evaporation.

Explanation:

The heat from the sun provides energy to the liquid water molecules in the wet cloth. These molecules move faster and eventually escape into the air as water vapor (H2O(g)H_2O_{(g)}), leaving the cloth dry.