States & Particles
Which state of matter has particles that are tightly packed and mainly vibrate in place?
SOLID. Its particles are packed closely together and vibrate in place.
What usually happens to particle movement when thermal energy is added?
Particle movement INCREASES.
Which subatomic particle has a positive charge, and where is it located?
PROTON; it is located in the NUCLEUS.
Name one EXTENSIVE physical property—one that depends on the amount of matter present.
MASS, VOLUME, or WEIGHT.
Tearing a sheet of paper into smaller pieces is what type of change? Why?
PHYSICAL CHANGE. The size/shape changes, but no new substance forms.
Which state has a definite volume but takes the shape of its container?
LIQUID. Liquid particles remain close together but can slide past one another.
Name the phase change: LIQUID → SOLID. Is thermal energy added or removed?
FREEZING; thermal energy is REMOVED.
Which two particles are located in the nucleus?
PROTONS and NEUTRONS.
Name one INTENSIVE physical property that does not depend on the amount of matter present.
DENSITY, MELTING POINT, BOILING POINT, or SOLUBILITY.
Rust forming on metal is what type of change?
CHEMICAL CHANGE because new substance(s) form.
A substance has no definite shape and no definite volume. What state is it, and what are its particles doing?
GAS. Its particles are farther apart and move freely, spreading to fill the available space.
Name the phase change: GAS → LIQUID. What happens to particle movement?
CONDENSATION; particle movement DECREASES as thermal energy is removed.
What is an element?
A pure substance made of only ONE kind/type of atom.
Calculate the density: mass = 24 g and volume = 8 cm³.
3 g/cm³. Density = mass ÷ volume = 24 ÷ 8.
Give two observations that can be evidence of a chemical change.
Any two appropriate clues: gas production, unexpected temperature change, light, formation of a solid/precipitate, lasting/unexpected color change, or odor change.
Why can a liquid change shape while a solid keeps its own shape?
Liquid particles can move/slide past one another. Solid particles are held in fixed positions and mainly vibrate.
A puddle disappears on a warm afternoon. Identify the phase change and explain the energy change.
EVAPORATION: liquid → gas. Thermal energy is added and particle movement increases.
What is the difference between a molecule and a compound?
A MOLECULE is two or more atoms bonded together. A COMPOUND contains two or more DIFFERENT elements.
Sample A has mass 20 g, volume 10 cm³. Sample B has mass 40 g, volume 20 cm³. Could they be the same pure substance? Explain.
YES. Both have a density of 2 g/cm³. Mass and volume changed with amount, but density remained the same.
A reaction in an open cup appears to lose mass because a gas escapes. Was matter destroyed? Explain.
NO. Matter was not destroyed; some matter left the OPEN SYSTEM as gas. Matter is conserved.
A student says, “Particles in a solid do not move.” Correct the student using the particle model.
Solid particles DO move: they vibrate in place. They do not freely move past one another like liquid or gas particles.
Dry ice changes directly from a solid to a gas. Name the phase change and describe what happens to thermal energy and particle motion.
SUBLIMATION. Thermal energy is added and particle movement increases as the substance changes solid → gas.
Model A is 🔵—🔵. Model B is 🔵—🔴. Which model is a molecule? Which represents a compound? Explain.
BOTH are molecules because atoms are bonded. Model B also represents a COMPOUND because it contains different types of atoms/elements.
Why is density generally more useful than mass alone when identifying an unknown pure substance?
Density is an INTENSIVE property that does not depend on sample amount; mass is EXTENSIVE and changes when the amount changes.
Why is a closed system useful when studying conservation of matter during a chemical reaction?
Why is a closed system useful when studying conservation of matter during a chemical reaction?