# Water cycles and Changes in State

# Factors Affecting Rate of Evaporation

This science revision note aims to help your child understand how to explain evaporation concepts clearly.

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Rachel conducted an experiment. She had three different containers with an equal volume of water in each, as shown in the diagram below. She left the containers open for 20 minutes under the hot sun.

After 20 minutes, which of the containers (A, B or C) would contain the least volume of water? Explain your answer.

__STEP 1__

Identify the **factor affecting the rate of evaporation** that is being **changed** here.

In the lesson notes, your child has learnt 3 factors affecting rate of evaporation.

- Presence of
**W**ind **E**xposed surface area**T**emperature of the liquid

We use the acronym **WET**.

Now, we have to identify which is the relevant factor for the above question.

- The
**temperature**of water: As all containers were placed in the same place, this factor is not changed. - Presence of
**wind**: As all containers were placed in the same place, this factor is not changed. **Exposed****surface****area**of water: The shapes of the containers are different and their openings are of different sizes, as seen by the diagram. Hence, the**exposed surface area of water is the factor being changed**.

__STEP 2__

Explain how the factor changed affects the rate of evaporation.

How does exposed surface area affect rate of evaporation? **The greater the exposed surface area of water, the faster the rate of evaporation, the ****lower the volume of water left at the end of the experiment.**

__Step 3__

Identify which container will contain the least volume of water after 20 minutes.

Let’s work backwards: **Least water left the**** fastest rate of evaporation the**** greatest exposed surface area**

Which container has the greatest exposed surface area?

Container B

Hence, **Container B will contain the least volume of water after 20 minutes.**

__FINALLY, put your answers together.__

Question: After 20 minutes, which of the containers (A, B or C) would contain the least volume of water? Explain your answer.

**Answer: Container B will contain the least volume of water after 20 minutes. Container B has the greatest exposed surface area, so the water in Container B has the fastest rate of evaporation. **Hence, Container B will have the least volume of water left after 20 minutes.

**Note**: Your answer must state the factor affecting the rate of evaporation. For this question, the relevant factor is exposed surface area.

**Common mistakes**

**Wrong** answer: Container B will contain the least volume of water after 20 minutes. Container B has a greater exposed surface area, so the water in Container B has a faster rate of evaporation. Hence, Container B will have less water left after 20 minutes.

Since you are comparing **more than two containers**, you have to use **superlatives** (eg. great__est__, fast__est__) to explain your answer!

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