TEAS Ready⚗️ Science · Chemistry · Lesson 2 of 6 · 5 min
States of matter and physical vs chemical change
🧊 Ice melting and a match burning both look like change, but only one makes a new substance. The TEAS loves asking which is which.
💡 Key idea
If the substance is still the same substance afterward, the change was physical; if something new formed, it was chemical.
🧠 The idea
Matter exists mainly as SOLID (fixed shape and volume, particles vibrating in place), LIQUID (fixed volume, takes the container's shape) and GAS (fills its container, particles far apart and fast). Adding energy drives melting (solid to liquid), vaporization (liquid to gas) and sublimation (solid straight to gas); removing energy drives freezing, condensation and deposition. During a phase change the temperature stays constant while energy goes into rearranging particles. A PHYSICAL CHANGE alters form or state but not identity: cutting, dissolving sugar, boiling water. A CHEMICAL CHANGE makes new substances with new properties: burning, rusting, cooking an egg. Signs of a chemical change include gas bubbles, a color change, light or heat released, or a precipitate forming. Physical properties (color, melting point, DENSITY) can be measured without changing the substance; chemical properties (flammability, reactivity) show up only in a reaction. Density = mass ÷ volume.
✏️ Worked example
A metal block has a mass of 54 g and a volume of 20 cm³. Step 1: density = mass ÷ volume. Step 2: 54 g ÷ 20 cm³ = 2.7 g/cm³. Step 3: water is 1.0 g/cm³, so the block (2.7) is denser and sinks. Cutting the block in half halves both mass and volume, so its density stays 2.7 g/cm³: density is an intensive property.
📌 Takeaways
- Solid → liquid → gas as energy is added; temperature holds steady during a phase change.
- Physical change keeps identity; chemical change makes a new substance.
- Density = mass ÷ volume, and it does not depend on sample size.
📖 Terms in this lesson
Physical change: A change in form or state that does not create a new substance; for example, ice melting into water.
✅ Check yourself
Question 1 of 3
Which is a chemical change?
- Ice cubes melting
- Paper burning
- Salt dissolving in water
- Glass shattering
Show the answer and rationale
Answer: B
Burning paper produces new substances (ash, carbon dioxide, water vapor) and releases heat and light, so it is chemical. Melting, dissolving and shattering change only form or state; the substance stays the same.
Question 2 of 3
Dry ice (solid carbon dioxide) turns directly into a gas. This phase change is called
- sublimation
- deposition
- condensation
- evaporation
Show the answer and rationale
Answer: A
Sublimation is solid going straight to gas without becoming a liquid. Evaporation starts from a liquid, condensation is gas to liquid, and deposition is the reverse of sublimation, gas to solid.
Question 3 of 3
A liquid has a mass of 30 g and a volume of 25 mL. What is its density?
- 5 g/mL
- 750 g/mL
- 1.2 g/mL
- 0.83 g/mL
Show the answer and rationale
Answer: C
Density = mass ÷ volume = 30 g ÷ 25 mL = 1.2 g/mL. Dividing volume by mass gives 0.83, subtracting gives 5, and multiplying gives 750; none of those is the density formula.
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