- What is the difference between temperature and heat?
- Temperature measures thermal energy, while heat is energy transfer between objects.
- Heat and temperature are the same thing with different names used interchangeably.
- Temperature only applies to liquids, while heat applies to gases and solids.
- Heat is measured in degrees, while temperature is measured in joules per unit mass.
Temperature measures the average kinetic energy of particles in a substance. Heat is the transfer of thermal energy from a hotter object to a cooler one. One hot object can transfer heat to many cold objects.
- What is the first law of thermodynamics?
- Heat always flows naturally from cold objects to hot objects without external work.
- Energy cannot be created or destroyed, only transformed.
- The total entropy of a system always increases.
- All substances freeze at the same temperature regardless of pressure or conditions.
The first law of thermodynamics is the law of energy conservation: Energy in a system equals work done plus heat added. Energy can change form but total energy is always conserved.
- What is thermal energy?
- The energy transferred from hot to cold objects
- The temperature of a substance measured in degrees
- The sum of kinetic energy from all particle motion
- The energy stored in chemical bonds of atoms
Thermal energy is the sum of kinetic energy from all the random particle motion in a substance. A hot object has more thermal energy than a cold object of the same mass.
- What does the second law of thermodynamics state?
- Energy is always conserved in all processes without any exceptions or losses.
- Heat always flows from cold objects to hot objects under normal conditions.
- All systems move toward greater disorder and entropy increases.
- Temperature and pressure are always equal in all substances and systems.
The second law of thermodynamics states that entropy (disorder) in an isolated system always increases. This explains why heat naturally flows from hot to cold, not the reverse.
- What is absolute zero?
- The theoretical temperature where entropy reaches zero and particles have only zero-point energy
- The lowest temperature that can be achieved using advanced cooling and refrigeration technology
- The temperature at which all atomic and molecular motion completely stops with no quantum effects
- The point on temperature scales where readings cannot go below zero on any measurement device
Absolute zero (0 Kelvin or −273.15°C) is the theoretical lowest temperature defined by the third law of thermodynamics. At absolute zero, entropy reaches its minimum, and particles have only zero-point quantum energy, though this state is unattainable in practice.
- Which factor has the greatest effect on the rate of heat conduction between two objects?
- The temperature difference between the objects
- The humidity of the air surrounding the objects
- The time of day when the heat transfer occurs
- The color of the surfaces in contact
The rate of heat conduction depends directly on the temperature difference between the two objects. A larger temperature difference causes faster heat transfer through conduction.
- What is entropy?
- The amount of heat energy in a system
- The measure of disorder in a system
- The rate of temperature change over time
- The efficiency of a heat engine
Entropy measures the disorder or randomness in a system. The second law states entropy always increases in isolated systems, meaning processes naturally move toward disorder.
- Which of the following is NOT a method of heat transfer?
- Conduction
- Convection
- Radiation
- Condensation
Condensation is a phase change from gas to liquid, not a method of heat transfer. Conduction, convection, and radiation are the three ways heat moves between objects.
- What is specific heat capacity?
- Energy required to raise one kilogram by one degree Celsius
- The temperature at which a substance melts
- The rate at which heat escapes from an object
- The maximum temperature a substance can reach
Specific heat capacity is the energy required to raise one kilogram of a substance by one degree Celsius. Water has high specific heat, which is why it takes a long time to heat or cool.
- What happens during a phase change?
- The temperature increases or decreases constantly.
- Energy is absorbed or released but temperature stays constant.
- The substance moves to a different location.
- The pressure of the substance increases dramatically.
During phase changes (melting, freezing, boiling, condensing), the temperature stays constant while energy is absorbed or released. This energy breaks or forms molecular bonds without changing temperature.
- Which words correctly complete both blanks?
- radiation/conduction
- convection/radiation
- conduction/convection
- conduction/radiation
Conduction is heat transfer through direct contact between objects. Convection is heat transfer through the movement of fluids (liquids or gases), such as air circulation in a room.
- What is the efficiency of a heat engine?
- The total amount of heat produced by fuel combustion
- The time it takes for the engine to heat up
- The percentage of heat energy converted to useful work
- The temperature at which the engine operates
Engine efficiency is the ratio of work output to heat input, expressed as a percentage. No real engine can achieve 100% efficiency due to heat loss and the second law of thermodynamics.
- What is internal energy in a system?
- The total kinetic and potential energy of all particles
- The external energy applied to move the system
- The heat energy the system can absorb from surroundings
- The temperature measured at the center of an object
Internal energy includes all the energy stored in a system’s particles: kinetic energy from their motion and potential energy from their interactions. It can be changed by heat transfer or work.
- How does pressure affect the boiling point of water?
- Higher pressure has no effect on boiling point.
- Higher pressure increases the boiling point of water.
- Higher pressure decreases the boiling point.
- Pressure only affects freezing point, not boiling point.
Higher pressure increases the boiling point because molecules need more energy to escape the liquid. Conversely, lower pressure decreases the boiling point, which is why water boils at lower temperatures at high altitudes.
- Why does the second law prevent perpetual motion machines?
- Friction is not present in perpetual motion machines.
- Energy input is infinite so machines never wear out.
- Entropy must increase, so systems lose usable energy as heat.
- Gravity decreases the efficiency of all machines.
The second law guarantees that entropy increases in any real process. Energy continuously converts to unavailable heat, so systems eventually lose their ability to do work. True perpetual machines are impossible.