Year 4 Science: The temperature at which water changes state
Part of the Year 4 Science changing state and the water cycle chapter. Chapter overview · whole chapter on one page
The temperature at which water changes state
Each material changes state at a particular temperature, which we measure in degrees Celsius (°C). For water, the important temperatures are:
| Water | Temperature (degrees Celsius) | What happens |
|---|---|---|
| Ice | 0 | melts to water, or water freezes to ice |
| Water | 100 | boils, and turns into water vapour |
Key ideas
- Water freezes at 0 degrees Celsius, and ice melts at 0 degrees Celsius.
- Water boils at 100 degrees Celsius.
- Temperatures are measured in degrees Celsius, with a thermometer.
- The temperature for a change of state is the same each time for the same material.
Method. Read the table.
- Read the table. Water freezes at the same temperature that ice melts.the same
- Read the number. That temperature is 0 degrees Celsius.0
- Write the answer. 0
Check. Ice melts at 0 degrees Celsius too. ✓
Method. Subtract the freezing temperature from the boiling temperature.
- Read the two numbers. Water freezes at 0 and boils at 100 degrees Celsius.0 and 100
- Subtract. 100 minus 0 is 100.100 - 0 = 100
- Write the answer. 100
Check. The range from freezing to boiling is 100 degrees. ✓
Method. Read the table.
- Read the boiling row. The boiling row says 100 degrees Celsius.100
- Check the picture. The right-hand end of the scale in the picture is also 100.right-hand end
- Write the answer. 100
Check. The scale in the picture ends at 100. ✓
Watch out
Watch out: a temperature of 0 degrees Celsius is not the same as no temperature. It is the temperature at which water freezes.
Try it at home or school (with a grown-up). Look at a kitchen thermometer, or a thermometer in a window, with a grown-up. Read the temperature in degrees Celsius. Do not touch any hot water, and never boil water yourself.
Exam tip
Grown-up tip. Ask: “What does the thermometer say? Is it above or below 0 degrees?” Let your child find 0 and 100 on a thermometer picture, and point to each one.
Exercise 7B The temperature at which water changes state
Method. Read the table in section 7.2.
- Read the freezing row. Water freezes at 0 degrees Celsius.0
- Write the answer. 0
Check. Zero degrees is the freezing point of water. ✓
Method. Read the table in section 7.2.
- Read the table. Ice melts at the same temperature as water freezes.same
- Write the answer. 0
Check. Ice and water change state at 0 degrees. ✓
Method. Read the table in section 7.2.
- Read the boiling row. Water boils at 100 degrees Celsius.100
- Write the answer. 100
Check. Boiling water is turning into water vapour. ✓
Method. Subtract 0 from 100.
- Read the numbers. Freezing is 0 and boiling is 100.0 and 100
- Subtract. 100 minus 0 is 100.100
- Write the answer. 100
Check. The difference is 100 degrees. ✓
Method. Read the scale.
- Read the end. The right-hand end of the scale says 100.100
- Write the answer. 100
Check. The scale goes from 0 to 100. ✓
Method. Read the table.
- Read the freezing row. The table says water freezes at 0 degrees Celsius.0
- Write the answer. yes
Check. Zero is the freezing point of water. ✓
Method. Think about measuring temperature.
- Think about the tool. A thermometer measures temperature in degrees Celsius.thermometer
- Write the answer. thermometer
Check. A ruler measures length, not temperature. ✓
Method. Compare the two numbers.
- Read the numbers. The numbers are 20 and 0.20 and 0
- Choose the bigger. The bigger number is the hotter temperature, so it is 20.20
- Write the answer. 20
Check. Twenty is above zero, so it is warmer. ✓
Method. Check the boiling temperature.
- Read the table. The table says water boils at 100 degrees Celsius.100
- Decide. 50 is not the boiling temperature, so the child is not right.no
- Write the answer. no
Check. Water boils at 100 degrees Celsius. ✓
Method. Check the freezing temperature.
- Read the table. Water freezes at 0 degrees Celsius.0
- Decide. So Ruby is not right.no
- Write the answer. no
Check. Ten degrees is warmer than freezing. ✓
Method. Think about a fair test.
- Think about the test. Only the temperature you measure should change, so the thermometer and the ice should stay the same.stay the same
- Write one thing. For example, use the same thermometer each time.same thermometer
- Write the answer. Accept any one thing, such as: the same thermometer, the same ice cube, or the same place to measure.
Check. A fair test keeps everything else the same. ✓
Method. Think about what the thermometer measures.
- Think about the bulb. The bulb measures the temperature of what it touches.touches
- Write the reason. If it touches the cup, it measures the cup, not the water.the cup
- Write the answer. Accept any sentence that says the bulb must be in the water to measure the water, and not the cup.
Check. A thermometer must measure the right thing. ✓