Changes of State
What is the process called when a solid becomes a liquid?
Melting
Which state of matter has particles that vibrate but remain in fixed positions?
Solid
What is the transfer of thermal energy from a warmer object to a cooler one called?
Heat
What is the melting point of water in Celsius?
0°C
Name the types of heat transfer described below:
1. The transfer of heat through direct contact
2. The transfer of heat through liquids or gases
3. The transfer of heat through electromagnetic waves
1. Conduction
2. Convection
3. Radiation
The process when a liquid changes to a gas.
Evaporation
Why does a liquid take the shape of its container while a solid does not?
Liquid particles slide past each other with no fixed positions; solid particles are locked in place.
How is thermal energy different from temperature?
Thermal energy = total energy of all particles
Temperature = average motion of particles.
The temperature at which a liquid changes to a gas
Boiling point
Which state of matter does not require matter to transfer?
Radiation
What change of state happens when a gas becomes a liquid, and what causes it?
Condensation; caused by loss of thermal energy.
Compare the motion of particles in a liquid versus a gas.
Liquid = particles slide but stay close together
Gas = particles move freely and spread apart in all directions.
Which has more thermal energy: a bathtub of warm water or a cup of boiling water? Explain.
The bathtub, because it has more particles, so its total energy is greater despite lower temperature.
Thermal Energy
Compare how heat travels by conduction and radiation.
Conduction needs direct contact of particles; Radiation transfers energy through electromagnetic waves and can occur in empty space.
The process of changing from a gas to a liquid
Condensation
Which state of matter generally has the lowest density, and why?
Gas, because particles are spread far apart with much empty space between them.
Explain how removing heat from a system changes both the thermal energy and particle motion.
Removing heat lowers the total energy, slows particle motion, reduces temperature, and may cause phase changes.
What must decrease for liquid water to freeze?
Thermal energy (and particle motion)
How do convection currents form in the atmosphere or oceans?
Warm, less dense fluids rise while cooler, denser fluids sink, creating continuous circulation.
Why is melting considered a physical change and not a chemical change?
Because it changes the state of matter, not the substance.
What happens to particle motion when thermal energy is removed?
Particle motion slows down, lowering temperature and possibly changing state
Apply the Law of Conservation of Energy to explain why the following scenario happens:
You place your hand on the school desk and it feels cold. After a while, it stops feeling cold and feels like the same temperature as your hand.
Answer: Energy transfers from your warmer hand to the colder desk until thermal equilibrium is reached; no energy is lost, only transferred.
Particles vibrate in place as a solid, slide past one another as a liquid, and move freely/spread out as a gas, increasing motion with added energy
A pot of water is boiling on a stove. Describe where conduction, convection, and radiation each occur in this system.
Conduction = stove burner → pot
Convection = water circulates inside pot
Radiation = heat through infrared waves/fire is emitted from burner and pot to surroundings