P3 - Heating and Cooling Graphs

What is internal energy?

The total energy stored inside a system by its particles, including kinetic and potential energy.

What two types of energy make up internal energy?

Kinetic energy (movement of particles) and potential energy (due to intermolecular forces and chemical bonds).

What does a heating graph show?

It shows how the temperature of a substance changes as it is heated and changes state.

What does a cooling graph show?

It shows how the temperature of a substance decreases as it cools and changes state.

What happens to temperature during a change of state?

The temperature stays constant even though energy is still being added or removed.

What happens to internal energy during a change of state?

Internal energy increases (when heating) or decreases (when cooling) because energy is used to break or form intermolecular forces.

What does a horizontal line mean on a heating or cooling graph?

A change of state is occurring (melting, boiling, freezing, condensation, etc.).

What happens during the flat section of a heating graph?

The substance is changing state; energy is being used to overcome intermolecular forces, not increase temperature.

What is melting?

When a solid changes to a liquid.

What is boiling?

When a liquid changes to a gas.

What is freezing?

When a liquid changes to a solid.

What is condensation?

When a gas changes to a liquid.

What is sublimation?

When a solid changes directly into a gas without becoming a liquid first.

What is the melting point?

The temperature at which a substance changes from solid to liquid.

What is the boiling point?

The temperature at which a substance changes from liquid to gas.

How can you find the melting point on a heating graph?

By reading the temperature at the start of the first flat (horizontal) section.

How can you find the boiling point on a heating graph?

By reading the temperature at the start of the second flat (horizontal) section.

What does a rising line on a heating graph represent?

An increase in temperature as energy is added to increase kinetic energy of particles.

What does a falling line on a cooling graph represent?

A decrease in temperature as energy is removed, reducing particle movement.

Why doesn't temperature change during melting or boiling?

Because energy is used to break intermolecular forces rather than increase kinetic energy.

Why doesn't temperature change during freezing or condensing?

Because energy is being released as intermolecular forces form.

Is energy being transferred during a change of state?

Yes, energy is still being transferred even though temperature remains constant.

What is latent heat?

The energy required for a substance to change state without changing temperature.

What is the name of the energy needed to melt or boil a substance?

Latent heat.

Are changes of state physical or chemical changes?

Physical changes.

Why are changes of state physical changes?

Because the substance can return to its original state with no new substance formed.

What is the key feature of a physical change?

It is reversible, and no new substance is formed.

Do particles gain or lose energy during melting and boiling?

Gain energy.

Do particles gain or lose energy during freezing and condensation?

Lose energy.

What state change occurs at the first plateau on a heating graph?

Melting (solid to liquid).

What state change occurs at the second plateau on a heating graph?

Boiling (liquid to gas).

What state change occurs at the first plateau on a cooling graph?

Condensation (gas to liquid).

What state change occurs at the second plateau on a cooling graph?

Freezing (liquid to solid).

What remains constant during the plateaus on a graph?

Temperature.

What increases during the sloped sections of a heating graph?

Temperature and kinetic energy of particles.