Which row describes the arrangement and motion of the particles in a liquid?
| arrangement | motion | |
|---|---|---|
| A | random and particles are touching | moving slowly |
| B | random with space between all particles | moving slowly |
| C | an ordered lattice with all particles touching | moving slowly |
| D | an ordered lattice with space between all particles | moving quickly |
▶️ Answer/Explanation
Ans: A
In a liquid, particles are close together (touching) but arranged randomly, not in a lattice. They move slowly compared to gas particles but faster than solid particles. Option A correctly describes this arrangement and motion.
Option B is incorrect because there isn’t space between all particles in a liquid. Option C describes a solid (ordered lattice). Option D describes a gas (space between particles and fast motion).
Oxygen melts at –219°C and boils at –183°C.
At which temperature is oxygen a liquid?
A) –225°C
B) –189°C
C) –175°C
D) 25°C
▶️ Answer/Explanation
Ans: B
To determine when oxygen is a liquid, we need to find a temperature between its melting point (–219°C) and boiling point (–183°C).
Let’s evaluate each option:
A) –225°C: Below melting point → solid state
B) –189°C: Between –219°C and –183°C → liquid state (correct answer)
C) –175°C: Above boiling point → gaseous state
D) 25°C: Far above boiling point → gaseous state
Therefore, the only temperature where oxygen exists as a liquid is –189°C.
The pressure of a sample of gas is decreased. The temperature is kept constant.
Which row describes the effects on the particles?
| movement of particles | collisions between particles | |
|---|---|---|
| A | slower | occur less often |
| B | slower | occur with more force |
| C | no change in speed | occur less often |
| D | no change in speed | occur with more force |
▶️ Answer/Explanation
Ans: C
When the pressure of a gas decreases at constant temperature:
1. Particle speed: The temperature remains constant, so the average kinetic energy of the particles doesn’t change. This means their speed stays the same.
2. Collision frequency: Lower pressure means the gas expands, so particles are farther apart. This results in fewer collisions because they have more space to move between collisions.
Looking at the options:
A & B: Incorrect because particle speed doesn’t change (temperature is constant)
D: Incorrect because collisions don’t occur with more force (temperature is constant)
C: Correct – speed remains the same and collisions occur less often
A sample of ethanol is left in an open beaker at room temperature.
After 24 hours, no ethanol remains in the beaker.
What has happened to the ethanol?
A) It has boiled.
B) It has condensed.
C) It has evaporated.
D) It has frozen.
▶️ Answer/Explanation
Ans: C
At room temperature, ethanol is a volatile liquid that will gradually evaporate when left in an open container. Boiling requires heating to the boiling point (78°C for ethanol), condensation is the opposite process (gas to liquid), and freezing would leave solid ethanol behind. Since the ethanol completely disappeared over time without any heating, the correct answer is evaporation.