Water Cycles and Changes In State

Explain Condensation Process

This science revision note aims to help your child explain the condensation process using proper scientific keywords.

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Take note of the MUST-KNOW condensation process

• Answering technique for condensation:

• • Warmer water vapour rises, comes into contact with the (cooler inner or outer surface), loses heat and condenses to form water droplets

• Identify the surface that condensation occurs on:

• • Inner or outer surface?
  • Cooler surrounding air (e.g. mist appearing in the air)

• Ways to increase the rate of condensation:
  • Increase rate of evaporation (boiling water, increase the flame size)
  • Make the cooler surface cooler (lower the temperature of the cooler surface by adding ice on it or place the cooler surface in the freezer first)

Let’s try out this question 🙂

The diagram below shows a cup filled with hot water. State where the water droplets will be found and explain your answer.

STEP 1

Explain how water vapour formed – we need to explain using the evaporation concept.

STEP 2

Identify the cooler surface – the inner or outer surface of the cup.

FINALLY, put your answer together

Question: State where the water droplets will be found and explain your answer.

Answer:

The water droplets will be found on the inner surface of the glass. The hot water will evaporate into warm water vapour. The warm water vapour rises, comes into contact with the cooler inner surface of the cup, loses heat to the inner surface and condenses into water droplets.

Common mistakes

Wrong answer: The hot water gained heat from the surrounding and evaporate into water vapour

Teachers’ comments: Look at the diagram carefully. The water is already at a higher temperature than the surroundings. Since heat flows from a warmer to a cooler region, hot water cannot gain heat from the surroundings.

Let’s try another question!

Practice makes perfect! 🙂 

Try out this question.

What do you notice?

The same answering technique (reasoning) on condensation is used!

Question

Sarah has a container of water. The water is 70°C. She closed the container and placed it on her kitchen table. After 10 minutes, she noticed there were tiny water droplets on the container. Did the water droplets form on the inner or outer surface of the container? Explain your answer.

STEP 1

Consider how water droplets are formed.

Water droplets are formed when warmer water vapour comes into contact with a cooler surface.

Take note of the word “warmer” and “cooler”. Which is at a higher temperature? the warmer water vapour. Hence, our duty as science student is to find out where is the warmer water vapour.

STEP 2

Identify which side of the container has warmer water vapour, the outside or inside.

To do this, consider the temperature of the water vapour on both sides:

• Outside: As the container was placed in the kitchen, the surrounding air is at room temperature, hence water vapour on the outside of the container is at room temperature, which is around 25°C
• Inside: The 70°C water in the container will evaporate into warm water vapour. The water vapour inside the container is higher than room temperature

Since the water vapour inside the container is warmer than the water vapour outside the container, water vapour inside the container will condense when it comes into contact with the cooler inner surface of the container.

STEP 3

Explain how the warmer water vapour forms water droplets.

Makes sure you include each of the points:

• Warmer water vapour in the container comes into contact with the cooler inner surface of the container
• The water vapour loses heat
• And condenses into tiny water droplets on the inside of the container

FINALLY, put your answer together

Question: Did the water droplets form on the inner or outer surface of the container? Explain your answer.

Answer:

Water droplets formed on the inner surface of the container.

The hot water in the container will evaporate into warm water vapour. The warmer water vapour in the container rises and comes into contact with the cooler inner surface of the container. The warmer water vapour loses heat and condenses into tiny water droplets on the inside of the container.

Note: You need to include the evaporation concept. 

Common mistakes

Incomplete answer: Water vapour loses heat and condenses to form water droplets.

Teachers’ comments:

• Where is the source of water vapour? You need to explain the evaporation concept first.
• The explanation of the condensation concept misses important details. The words missing include “warmer water vapour inside the container” and “cooler inner surface of the container”. 

Wrong answer: Water evaporates and condenses to form water droplets.

Teachers’ comments:

• Water cannot evaporate and condense at the same time! The student is using the sentence connector wrongly. A good method is to break up the concept into different sentences. 

Another wrong answer: Water droplets formed on the outer surface of the container. The surrounding air is colder than the air in the container, hence the outer surface of the container is cooler than the inner surface. Thus, water vapour on the outside will come into contact with the cooler outer surface, lose heat and condense into tiny water droplets.

Teachers’ comments:

• Condensation happens due to the difference in temperature between the water vapour and the surface, where the water vapour has to be warmer than the surface. This means that you cannot only compare the temperature of the different surfaces, you also have to compare the temperature of the water vapour on both sides, to see which side will have the greater difference in temperature between the water vapour and the surface.

Note: The greater the difference in temperature between the water vapour and the cooler surface, the faster the rate of condensation.

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✍️ Read this revision notes on which side condensation takes place.

We will share a technique that your child can use to quickly identify the correct side where condensation takes place.

>>> https://scienceshifu.com/science-revision-notes-on-condensation/

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