Chapter 24: Foundations of Chemistry Lesson 24.3: Physical Changes Pages 950 - 957 Lesson Objectives: Students will be able to define what is a physical change Students will demonstrate understanding of changes in the state of matter. Students will be able to state that dissolving is a physical process Students will be able to recognize that mass is conserved during a physical change

Scientific Vocabulary and Other Keywords Melting Boiling Change of state Thermal energy Sublimation Deposition Dissolving Conservation of Mass Scientific words Physical change

Although the sand has changed shape…. It is still sand. An artist changed a flat area of sand into a masterpiece that looks very different. Is it still sand? Yes! Although the sand has changed shape…. It is still sand.

A physical change is a change in size, shape, form, or state of matter in which the matter’s identity stays the same.

Changing state of water Matter such as water can change into three physical states: Solid Liquid Gas STEAM ICE WATER In order to change the state of water, there needs to be: Movement of particles Thermal energy added or removed

THERMAL ENERGY Solid, Liquid and Gases What causes the state of matter to change? Regular arrangement of particles in a Solid

Adding Thermal Energy – Solid to a liquid When thermal energy is added to a solid, the particles move faster. The particles in the solid vibrate more, as they gain more energy The forces that are holding the particles together become weaker The particles are able to move more freely and the solid changes to a liquid. This is known as the MELTING POINT The melting point is the temperature at which a solid changes to a liquid

Adding Thermal Energy – liquid - gas Once the solid has melted, adding more thermal energy will cause the particles move and vibrate even faster. They move so fast that the forces holding them together, break apart. The particles are then able to break free and spread out as they form a gas. This is known as the BOILING POINT The boiling point is the temperature at which a liquid changes to a gas and the particles spread out

When thermal energy is added to matter, there will be a change of state.

Sublimation Unlike water, some substances that a solid, can change directly from a SOLID to a GAS, without changing to a liquid. This is called SUBLIMATION Sublimation of Iodine Solid Iodine changes directly from a solid to a gas when heated.

Removing the Thermal Energy (Losing energy) When thermal energy is removed, the temperature decreases and there is less energy available to the particles. The particles will now move much slower. When enough thermal energy is removed one of several processes may happen: Freezing Condensation Deposition

Freezing happens when the thermal energy is removed and the particles are moving so slowly the forces between the particles hold them tightly together Freezing and melting are REVERSE processes and happen at the same temperature. When thermal energy is removed from a gas, the particles move slowly and the forces between them get stronger. Liquid is formed. Boiling and condensation are REVERSE processes and happen at the same temperature. Deposition is the change from a GAS directly to a SOLID. It is the opposite of sublimation

Summary: Adding thermal energy Removing thermal energy

Dissolving Sugar Solution If you add sugar to water, eventually the sugar disappears. It has DISSOLVED. But it is still there. Dissolving is a physical change. Sugar Water Sugar Solution

= Conservation of Mass Sugar Solution 155.0g The mass of what is made is identical to the mass of the substances that you started with. Sugar 5.0g Sugar Solution 155.0g Water 150.g =

Question: If a sample of water has a mass of 200g and the final solution has a mass of 230g, how much solute dissolved in the water? 30g

Question: Which never changes during a physical change? a. State of matter b. Temperature c. Total mass d. Volume