Grade 6 - Science - Chapter 3 - Section 2

Changes of State

• A change of state occurs when a substance changes from one state of matter to another. • Changes of state include: • condensing (gas to liquid) • freezing (liquid to solid) • melting (solid to liquid) • evaporating (liquid to gas) • A change of state involves a transfer of heat from one substance to another. • When a substance melts or boils, it gains energy. When a substance condenses or freezes, it loses energy.

What is Heat?

• Heat is the energy that is transferred between objects that are at different temperatures. • Heat energy is always passed from an object with a higher temperature to one with a lower temperature. • When you touch something hot, heat flows from the object to your finger.

What is Temperature?

• Temperature is a measure of the average kinetic energy of the particles in an object. • All matter is made up of constantly moving particles, such as atoms or molecules. • When a particle is in motion, it has kinetic energy. • The more kinetic energy the particles have, the higher the temperature of the substance. • Particles in a substance move at random and at different speeds. The average of all these speeds is the average kinetic energy. • Temperature does not depend on the amount of particles in a substance.

heat

the energy transferred between objects that are a different temperatures

thermal energy

the kinetic energy of a substance's atoms

temperature

a measure of how hot (or cold) something isl; specifically, a measure of the average kinetic energy of the particles in an object.

radiation

the transfer of energy as electromagnetic waves

conduction

the transfer of energy as heat through a material

States of Matter

• The states of matter are the physical forms in which a substance can exist. • The three states of matter are solid, liquid, and gas. • A substance's state depends on the speed of its particles, the attraction between them, and the pressure around them. • A substance's chemical composition also influences the state it is in at a given temperature. • For example, milk is a liquid at room temperature, but butter is a solid.

How Heat Is Transferred: Convection

• The transfer of heat due to the movement of matter is called convection. • When you boil water, heat is passed from the burner to the pot and from the pot to the water by conduction. • As the water is heated, it becomes less dense. • Cooler, denser water at the top of the pot sinks. • This forces the warmer water to the surface. • Water continues to rise and fall in a circular pattern called a convection current.

How Heat Is Transferred: Conduction

• The transfer of heat from one object to another through direct contact is called conduction. • Heat flows from the particles of hot soup to the part of the spoon that is in the soup. • Heat travels from particle to particle, from the soup all the way up the spoon's handle.

How Heat Is Transferred: Radiation

• The transfer of heat or other energy as electromagnetic waves, such as visible light or infrared waves, is called radiation. • Radiation can occur between objects that are not in direct contact with each other. • The sun transfers energy through space by radiation.

Thermal Energy

• Thermal energy is the total kinetic energy of the particles that make up a substance. • Thermal energy, which is expressed in joules (J), depends partly on temperature. • Something at a high temperature has more thermal energy than something at a low temperature. • Thermal energy also depends on the amount of particles in a substance. • The more particles in a substance at a given temperature, the greater the thermal energy.

Thermal Expansion

• When particles move faster, they move apart. • As the space between the particles increases, the substance expands. • Therefore, an increase in temperature leads to an increase in volume. This is called thermal expansion. • When particles move faster, they move apart. • As the space between the particles increases, the substance expands. • Therefore, an increase in temperature leads to an increase in volume. This is called thermal expansion.

Reaching the Same Temperature

• When things that have different temperatures come into contact, energy will always be transferred. • Energy will pass from the warmer to the cooler object until both have the same temperature.