Notes
Properties and changes
- Physical properties (density, melting point, color) can be observed without changing the substance. Chemical properties (flammability, reactivity) describe changes into new substances.
- A physical change keeps the substance's identity. A chemical change forms new substances, shown by gas, color change, precipitate, light or heat.
States and phase changes
- Solids have definite shape and volume, liquids have definite volume, and gases have neither. Particle motion increases with temperature.
- Melting, vaporization and sublimation absorb energy; freezing, condensation and deposition release it. Temperature stays constant during a phase change.
Gas behavior
- Boyle's law: $P_1V_1 = P_2V_2$ at constant temperature.
- Charles's law: $\displaystyle \frac{V_1}{T_1} = \frac{V_2}{T_2}$ at constant pressure, with temperature in kelvin (K = C + 273).
Classifying matter
- Elements and compounds are pure substances. Mixtures are physical combinations and can be separated by physical methods.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Baking forms new substances.
Added energy goes into changing particle arrangement, not temperature.
$2 \times 12 = 3 \times V_2$, so $V_2 = 8$ L.
Charles's law: volume doubles when kelvin temperature doubles.
Melting point can be measured without forming a new substance.
The different parts are visible and unevenly mixed.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A sealed syringe holds 20 mL of air at 1 atm. A student pushes the plunger until the pressure is 4 atm. The temperature stays constant.
(a) Name the gas law that applies and state the relationship between pressure and volume.
Show the answer and scoring guide
Boyle's law. At constant temperature, pressure and volume are inversely related: when pressure goes up, volume goes down.
Check off the points you earned:
(b) Calculate the new volume of the air.
Show the answer and scoring guide
$P_1V_1 = P_2V_2$, so $1 \times 20 = 4 \times V_2$, and $V_2 = 5$ mL.
Check off the points you earned:
(c) Use particle motion to explain why the pressure increases as the volume decreases.
Show the answer and scoring guide
The same particles are squeezed into a smaller space, so they hit the walls more often. More collisions per second means greater pressure.
Check off the points you earned: