2. Physical Properties of Matter
A physical property is a characteristic of a pure substance that can be observed without changing it into another substance
-Physical state
-Temperature for freezing, boiling, or vaporizing
-Ability to dissolve in water
-Hardness, texture, color, and flexibility
Can be used to classify matter (ex. Metals are flexible and can conduct heat and electricity)

3. Chemical Properties of Matter
Chemical properties are characteristics of a pure substance that describe its ability to change into different substances
-Properties can be used to classify substances
-Examples: Ability to burn and/or react with other substances
Only observed when the original substance is changed into a different substance
-New substances may have different properties then the original substances

4. Changes in Matter
Matter can undergo two basic types of changes- physical changes and chemical changes
Physical changes- alters the form or appearance of matter but does not form any new substances
Chemical changes- changes in matter that produce one or more new substances

5. Physical Changes of Matter
A substance that undergoes a physical change is still the same substance after the change
A change in state, such as from a solid to a liquid or from a liquid to a gas, is an example of a physical change

6. Chemical Changes in Matter
A substance undergoing a chemical change is transformed into a different substance
In some chemical changes, a single substance changes into one or more other substances (ex. When hydrogen peroxide is poured on a cut it breaks down into water and oxygen gas)
In other chemical changes, two or more substances combine to form different substances (ex. Iron oxide forms when iron combines with oxygen in the air)
Unlike a physical change, a chemical change produces new substances with properties different from those of the original substances

7. Evidence of Chemical Change
Changed in energy and changes in properties are both signs that a chemical reaction has occurred
Observable changes can indicate a chemical change has occurred
Color Change-
May signal that a new substance has formed in an otherwise unchanged object (ex. Bread is browned when toasted)
Gas production-
Gases can be produced when solid or liquid reactants chemically combine (ex. Vinegar & baking soda produce carbon dioxide bubbles)
Formation of a precipitate-
Mixing two liquids can produce a precipitate, which is a solid that forms from the liquids (ex. Mixing milk & lemon juice forms a chunky precipitate called curds)

8. Observing Chemical Change
Properties of Copper
Pennies are coated with copper. Which are physical properties of copper and which are the chemical properties? What are two additional properties?

9. Chemical Reactions
A Chemical reaction- (also called a chemical change) is a change that produces one or more new substance
Occur when existing bonds break and new bonds form
Atoms and molecules rearrange to form new substances

10. Components of a Chemical Reaction
Chemical reactions can be represented with equations that show the different substances are undergoing the chemical change
When reactants combine, or breakdown, new products form
Reactants- Substances that enter into a chemical reaction and undergo change
Products-Substances formed as a result of a chemical reaction
Examples of Chemical reactions
2H + O → H₂O H₂O₂ → 2 H₂O + O₂
reactants → products reactants → products
Atoms present in the reactants are all present in the products
This means that the total number of atoms is the same (conserved) before and after the reaction occurs

11. Getting Chemical Reactions Started
Reactants need a initial push to get going
Activation energy – The minimum amount of energy needed to start a chemical reaction
Once the reaction is underway, it will either need more energy to keep going or it will release energy

12. Exothermic vs. Endothermic Reactions
Some chemical reactions require energy in the form of heat, while others give off energy
Reactions are classified as exothermic or endothermic based on the direction of heat flow
Exothermic Reactions
The energy released, as the products form, is greater that the energy required to break the bonds of the reactants
The energy is usually released as heat (ex. Natural gas releases heat when it burns
Endothermic Reactions
When more energy is required to break the bonds of the reactants than is released by the formation of the products
Often draws energy from the surroundings, leaving them cold (ex. When baking soda and vinegar combine, it absorbs heat from the surrounding air)

13. Rates of Chemical Reactions
Chemical reactions don’t all occur at the same rate
Reactions rates depend of condition such as surface area, temperature, concentration, and the presence of catalysts or inhibitors
Surface Area- Increasing the surface area of a substance will speed up reaction times
Temperature- Warm substances have faster reaction rates due to the particles having more initial energy
Concentration- A measure of the amount of each substance in the reaction
Reaction rates increase when there are higher concentrations, as there are more particles to react

14. Rates of Chemical Reactions Continued
Catalysts-
Substances that cause or accelerate a chemical reaction without being affected themselves
Increase reaction rates by lowering the activation energy needed to start a reaction
Inhibitors-
Materials used to decrease the rate of chemical reactions (ex. Preservatives)

15. Describing Chemical Reactions
Chemical Formulas
The formula of a compound identifies the elements in the compound and the ratio in which their atoms or ions are present. What are the missing chemical formulas in the table?

16. Describing Chemical Reactions
Modeling a Chemical Equation
Like a skateboard, a chemical equation has a basic structure. How many complete skateboards can be made from the parts pictured? 12 6 3 3

17. Describing Chemical Reactions
Molecules of nitrogen (N2) and hydrogen (H2) react to form ammonia (NH3). How many H2 and N2 molecules are needed to yield two molecules of NH3? 1 3
Nitrogen atom = Hydrogen atom =

18. Conservation of Mass
Law of conservation of mass- The principle that the total amount of matter is neither created nor destroyed during any chemical or physical change
No mass is lost or gained during a chemical or physical change
Since mass measures matter, this law is sometimes called the law of conservation of matter

19. Describing Chemical Reactions
Conservation of Mass
In a chemical reaction, matter is not created or destroyed. What is the mass of iron sulfide produced by this reaction?