thermal energy

kms

what does the particle theory of matter state

All matter is made up of particles. Particles are always moving. Temperature affects the speed at which the particles are moving.

Solid - distance + movement

Particles are held tightly together in a fixed shape. Particles are slowly vibrating but attractive forces between particles prevent them from moving.

Liquids - distance + movement

Particles are loosely packed. Particles are moving and can overcome some of the attractive forces between them, meaning they can slide past each other.

Gas - distance + movement

Particles are relatively far apart. Particles are moving quickly. The kinetic energy of the particles is greater than the attractive force between them, meaning particles can move farther apart and move freely of each other.

temp vs heat vs thermal energy

Temperature is a measure of the average kinetic energy of the particles in a substance. Temperature provides a comparative measure of how hot or cold an object is. If the temperature of two objects is known, the direction of heat transfer can be determined. (unit = °C, K (kelvins))

Heat is a form of energy transfer. Heat is energy transferred between two systems due to a temperature difference. Heat flows from the warmer object to the cooler one until both objects reach thermal equilibrium (same temperature). Heat cannot be measured but it can be calculated.

Thermal energy is the total kinetic energy of all particles in a substance. Substances with high energy are hot because particles are moving quickly. Substances with lower energy are cold because of slower-moving particles.

• A bear with more water will hold more thermal energy than a beaker with less water at the same temperature.
  

What does thermal energy depend on?

Thermal energy depends on both the speed of particles and the number of particles.

- if a large container of water is at the same temperature as water in a smaller container, the water in the large container will have more thermal energy because there are more particles.

• If there are two containers of water of equal size, but different temperatures, the hotter water will have more thermal energy because their particles are moving more quickly.

Temperature does not depend on the amount of substance, thermal energy does.

What is the relationship between particle movement and the temperature of an object?

When particles move faster or slower, the object’s temperature will increase or decrease.

transfer of thermal energy

Heat always moves from a hot object to a cold object. When heating a liquid over a Bunsen burner, the hot gas from the Bunsen burner is transferring energy to the test tube, which transfers energy to the liquid through the glass.

positive heating

If the heating is positive, then energy is being ADDED to the object and it will become HOTTER. It may change into a HIGHER energy state (e.g. liquid to gas)

negative heating

If the heating is negative, then energy is being REMOVED from the system and it becomes COLDER. It may change to a LOWER energy state (e.g gas to liquid)

if the object feels hot

energy is transferred into your hands

if your hand feels cold

energy is transferred from your hands to the object

thermal energy transfer e.g. evaporating methylated spirits

The methylated spirits evaporated from the wrist. It needed to gain energy in order to move from a liquid to a gas state. The energy from the wrist flowed into the methylated spirits. The wrist becomes colder as the methylated spirits evaporate, indicating that heat energy was being transferred from the wrist to the methylated spirits.

heating using energy bar charts

refer to page 42 scipad

The initial state should have one unit of energy already. The final state will have the initial energy + added heat units. The heat will be drawn as an arrow in the system and will be the amount of units added to the final state.

If you’re showing something is cooling, draw the arrow pointing away from the system.

why is thermal energy shown in the initial state?

there is always some amount of thermal energy in objects (unless zero degrees kelvin)

bacon is placed into a frying pan (heat transfer question)

Direction of energy transfer: frying pan to bacon (hot to cold remember!)

Explanation:

The bacon experiences POSITIVE heating, causing its temperature to INCREASE. The energy has transferred from the frying pan to the bacon.

A hot pot is placed into a sink full of cold water (heat transfer questions)

Direction of energy transfer: Pot to cold water

Explanation:

The pot experiences NEGATIVE heating, causing its temperature to decrease. The energy has transferred from the pot to the water.

Conduction

The transfer of thermal energy through DIRECT contact between particles of a substance, without moving those particles to a new location.

When thermal energy is supplied to one end of an object, particles at that end start to move/vibrate more quickly, bumping into neighbouring particles and transferring their kinetic energy.

process of conduction

When particles at one end of a metal rod are heated, they begin to vibrate more. This causes them to bump into neighbouring particles, making these vibrate more rapidly. The process of particles bumping to neighbouring particles is continues along the metal rod. In this way, energy is conducted from the hot end of the rod to the cold end, until the entire rod is hot.

thermal conductor

A material that allows heat to be transferred within the material without any movement of the material itself.

An object’s ability to transfer thermal energy through conduction depends on its properties. Metals are excellent conductors of heat because they have free electrons that can move around easily, transferring kinetic energy from one part to another easily and quickly. The atoms in metals are packed closely together, enabling them to transmit kinetic energy vibrations more readily.

Thermal insulators

Prevents heat from moving from one place to another.

Object’s that done have free electrons, or have an atomic/molecular structure that restricts the flow of kinetic energy. This prevents heat from being easily or quickly transmitted.