Unit 2 - Change of State and Gas Laws

What happens to the internal energy of a system when it is heated?

• It fluctuates

• It remains constant

• It increases

• It decreases

Answer explanation

When a system is heated, its internal energy increases due to the added thermal energy, which raises the kinetic energy of the particles within the system. Therefore, the correct answer is that the internal energy increases.

During which process do molecules in a solid move away from their fixed positions?

• Boiling

• Melting

• Condensation

• Evaporation

Answer explanation

During melting, solid molecules gain energy and move away from their fixed positions, transitioning into a liquid state. This distinguishes melting from boiling, condensation, and evaporation, which involve different phase changes.

What occurs when a liquid gains enough energy to break its bonds?

• Condensation

• Melting

• Boiling

• Freezing

Answer explanation

When a liquid gains enough energy, its molecules move faster and can overcome the intermolecular forces holding them together. This process is called boiling, where the liquid transforms into vapor.

What is the temperature change during a phase change?

• It increases

• It decreases

• It fluctuates

• It remains constant

Answer explanation

During a phase change, such as melting or boiling, the temperature remains constant despite the addition or removal of heat. This is because the energy is used to change the state of the substance rather than increasing its temperature.

What is evaporation?

• The escape of high-energy molecules from a liquid's surface

• The condensation of gas

• The process of boiling

• The freezing of a liquid

Answer explanation

Evaporation is the process where high-energy molecules escape from the surface of a liquid into the gas phase. This distinguishes it from boiling, condensation, and freezing, which are different physical processes.

Which of the following increases the rate of evaporation?

• Increasing temperature

• Reducing airflow

• Lowering temperature

• Decreasing surface area

Answer explanation

Increasing temperature raises the kinetic energy of molecules, leading to more molecules escaping the liquid phase into the vapor phase, thus increasing the rate of evaporation. The other options do not promote evaporation.

What is the specific heat capacity?

• The energy required to raise the temperature of 1kg of a substance by 1°C

• The energy required to change state

• The energy required to boil a substance

• The energy required to freeze a substance

Answer explanation

The specific heat capacity is defined as the energy required to raise the temperature of 1kg of a substance by 1°C. This distinguishes it from energy changes related to state changes or phase transitions.

What happens to gas molecules when temperature increases at constant volume?

• They move slower

• They collide less frequently

• They collide harder and more frequently

• They exert less pressure

Answer explanation

When temperature increases at constant volume, gas molecules gain kinetic energy, causing them to move faster. This results in more frequent and harder collisions with the walls of the container, leading to increased pressure.

What is absolute zero in Celsius?

• -273°C

• -100°C

• 100°C

• 0°C

Answer explanation

Absolute zero is the theoretical lowest temperature possible, where molecular motion stops. In Celsius, it is defined as -273°C, making this the correct answer.

According to Boyle's Law, what happens to pressure when volume increases at constant temperature?

• Pressure fluctuates

• Pressure remains constant

• Pressure decreases

• Pressure increases

Answer explanation

According to Boyle's Law, pressure and volume are inversely related at constant temperature. Therefore, when the volume increases, the pressure decreases.