Chapter 11 – Lesson 3 Physical Changes

Physical change - is a change in the size, shape, form or state of matter in which the matter’s identity stays the same. Ex: When ice melts some of its properties change – state of matter, the shape, and temperature, but it is still water.  1. Changes in Shape and Size Changes in shape and size are physical changes. – The identity of the matter has not changed. Ex: Cut paper into a square – the shape has changed but it is still paper.  

2. Changes in State of Matter In order to change the state of matter of a substance we need to add or remove thermal energy to speed up/slow down the particles of matter.   Adding Thermal Energy When we add thermal energy to a solid – the particles begin to move faster and faster, and the temperature increases. 1. Melting point is the temperature at which a solid changes to a liquid. When we add thermal energy to a liquid – the particles begin to move faster and faster, and the temperature increases. 2. Boiling point is the temperature at which a liquid changes to a gas.

Removing Thermal Energy When we remove thermal energy from a gas – the particles begin to move more slowly and temperature decreases. 3. Condensation is the process when a gas becomes a liquid. When we remove thermal energy from a liquid – the particles begin to move more slowly and temperature decreases. 4. Freezing is the process when a liquid becomes a solid. Freezing and Melting are reverse processes – so they occur at the same temperature. The same is true for boiling and condensation. Another change in state is deposition – it is the change from a gas directly to a solid. (It is the state opposite of sublimation)

To get a substance to change phase – you add or remove thermal energy. Notice that during the phase change the thermal energy is being used to push or pull the molecules apart and not used to increase/decrease temperature.

Ex: Salt dissolving in water for a salt water aquarium. Dissolving is a physical change because the identities of the substances are not changed. Ex: Salt dissolving in water for a salt water aquarium. You can reverse the process by boiling the salt water causing the liquid to change to a gas (water vapor) and leaving the salt behind. RECAP – A physical change does not change the identity of the substance. CLUES (words that indicate a physical change may have occurred) – Chopping Dissolving Cutting Vaporization Breaking Sliced Melting Freezes Condenses Ripped Torn Evaporates

Chapter 11 Lesson 4 – Chemical Properties and Changes

Chemical Properties A chemical property is a characteristic of matter that can be observed as it changes to a different type of matter. Ex: Paper burning is a chemical change. You can observe the paper and watch it burn and turn into a different substance. Burning is a chemical property. Another chemical property is rusting. Comparing Properties All matter can be described using BOTH physical properties and chemical properties. EX: A wood log is solid, round in shape, heavy, and rough (physical properties). The wood also has the ability to burn and decompose (chemical properties).

Chemical Changes A chemical change is a change in matter in which the substances that make up the matter change into other substances with new physical and chemical properties - (A new substance is formed). Iron (Fe) will rust when it reacts with oxygen (O2) in the air to produce a new substance called iron oxide (Fe2O3) = rust.

Formation of bubbles (gas produced) Color Changes Signs of Chemical Change How do you know a chemical change has occurred – there are different signs or clues to look for? Formation of bubbles (gas produced) Color Changes Energy Changes (Thermal energy (HEAT) released, Light energy released) An odor Precipitate forms It is important to remember that these sings do not always indicate a chemical change – the only proof a chemical change has occurred is the formation of a new substance.

Using Chemical Formulas A useful way to understand what happens during a chemical reaction is to write an equation. A chemical equation shows the chemical formula for each substance. The formulas to left of the arrow indicate the reactants and the formulas to the right of the arrow represent the products. (products are the new substance(s) that are formed)

Physical vs. Chemical Change Recap: