Physical Science – Chapter 18 Study Guide Answers
Chapter Objectives
1. Define pure substances and mixtures.
Pure substances – type of matter with a fixed composition, element
or compound (composition is definite)
Mixtures – 2 or more substances that can be separated by physical
means (Composition is variable)
2. Identify elements and compounds.
Elements – pure substances in which all atoms have the same identity
Compounds – when 2 or more different elements combine in a fixed
proportion
3. Compare and contrast solutions, colloids, and suspensions.
Solutions – particles are so small they cannot be seen with a
microscope and will never settle out; light cannot pass through,
homogenous mixtures
Colloids – particles that are larger than those in solution but not
heavy enough to settle out; Ex: milk, light passes through/scatters
(Tyndall effect)
Suspensions – heterogeneous mixtures, contains liquid, particles will
settle if left undisturbed, Ex: pond water; will scatter light
4. Describe the phase and energy changes associated with STATE changes.
Changing states of matter (from solids, liquids, or gas to another
state), physical changes
Melting – solid to a liquid, add energy
Freezing: liquid to solid, releases energy
Vaporization: liquid to gas, add energy
 Boiling: throughout the liquid
 Evaporation: surface only
Condensation: gas to liquid, releases energy
Sublimation: solid to gas, adds energy
5. Identify substances using physical properties.
Physical properties – properties than can be observed without
altering identity of substance
Alterations in form but not identity
Density, freezing/melting point, color
6. Compare and contrast physical and chemical changes.
Physical changes – doesn’t change the identity, sometimes it is
reversible
Tear, folding, dissolving, grind, phase change
Chemical changes – changes the identity, produces something new,
not reversible
Burn, release a gas
7. Identify chemical changes.
Burn (flammability), Rust, Decay, Digest, Corrosion
1) Color change
2) Odor change
3) Temperature change
4) Bubbles produced (gas released)
5) Precipitate (new solid produced)
8. Determine how the law of conservation of mass applies to chemical changes.
Law = mass cannot be created nor destroy
Mass you start with is the same as you end
Key Concepts
9. Types of Physical Changes (give examples)
See #5, tear, break, grind, dissolve, bursting a balloon, crumpling
paper
10. Types of Chemical Changes (give examples)
See #7, color/dye your hair, release gases, eat & digest food, when
limestone reacts with acid rain, cooking
11. Homogenous mixtures
2 or more substances blended evenly throughout (Cannot see the
different parts)
Ex: soft drinks, solutions
12. Heterogeneous mixtures
Mixture in which different materials can be easily distinguished
Ex: pasta salad, fruit salad, concrete, granite
13. Tyndall effect
Scattering of light by colloid particles
14. Melting point & Freezing Point
Water’s melting/freezing point = 0C or 32F
Same temperature
15. Heat of fusion
the amount of energy required to change 1 kg of a substance from a
solid to a liquid at its melting point or released when a liquid is
changed to a solid at its freezing point
16. Heat of vaporization
the amount of energy required for 1 kg of the liquid at its boiling
point to become a gas; energy released during condensation when a
gas becomes a liquid
17. Three types of matter
Solid, gas, liquid (4th = plasma)