Curriculum
Science — Second Preparatory
Unit 1: Matter and Energy
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Unit 2: Matter and Chemical Reactions
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Unit 3: Energy Flow in Photosynthesis and Respiration
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Unit 4: Geological Processes
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Text lesson
Changes of State
Changes of State
Applications and worked examples
Applications and worked examples
Key points
Example 1: heat needed to melt ice.How much heat is needed to melt 0.2 kg of ice at 0 °C?
Solutionuse Q = m × L, where m is the mass and L is the latent heat of fusion.
Q = 0.2 × 336 = 67.2 kJ
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Example 2: heating water. | How much heat is needed to raise the temperature of 0.5 kg of water from 20 °C to 80 °C? The specific heat capacity of water is 4200 J/(kg·°C) | muchneededraisetemperature |
| Solution |
| changetemperature |
ΔT = 80 − 20 = 60 °C
Q = 0.5 × 4200 × 60 = 126000 J = 126 kJ
Example 3: boiling water.How much heat is needed to turn 0.1 kg of water at 100 °C into steam at 100 °C?
SolutionQ = m × L = 0.1 × 2260 = 226 kJ
Simple experiment→Put a few drops of alcohol on the back of your hand. You will feel cold as it evaporates. The evaporation takes heat from your skin, and the same effect happens when your body sweats.
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