Chemistry Unit:

Chemical Reactions

PHYSICAL PROPERTIES

Physical property – characteristic that can be observed without changing the composition of a substance

Appearance includes things that can be observed with the senses

States of matter – solid, liquid, or gas

Volume, mass, and density

Melting point, boiling point, and others

CHEMICAL PROPERTIES

Chemical property – characteristic that cannot be observed without altering the substance

Ability to burnTendency to rustReaction to other

substances such as acids and bases

PHYSICAL CHANGES

Physical change – form or appearance of matter changes, but composition stays the same.Change does not produce a new substance Shape can change, but substance does notDissolving a solid into a liquid is a physical

change

CHEMICAL CHANGES

Chemical change: a change in the substance’s compositionDuring a chemical reaction:

Energy may be gained or releasedColor can changeSubstances may change odorFormation of a gas or the precipitation of a

solid

CHEMICAL REACTION

Chemical Reaction – one or more substances are changed into a new substance, with new physical and chemical properties.

Chemical Changes result in a new substance with a new chemical formula

SIGNS OF A CHEMICAL CHANGE

Heat is released or absorbed, measured by a temperature change

Unexpected color changeRelease of a gas

odor, steam, or bubblesFormation of a precipitate

when a solid forms from reacting liquids

CHEMICAL EQUATION

Chemical Equation – represents the chemical combining of elements and/or compounds (reactants and their products)

Reactants – substances that are about to react on the left of an equation.

Products - the new substance(s) that are produced on the right

Reactants yield Products

CHEMICAL EQUATION CONTINUED

Coefficient – number that indicates how many compounds or elements are present in chemical reaction, written in front of the formula or symbol.

Subscript – smaller number written after a symbol that tells how many atoms are present in a compound

REVIEW CHEMICAL EQUATION

CH4 + 2 O2 → CO2 + 2 H2O

1. What are the reactants?

2. What are the products?

3. What is the term for the small 4 by the CH4 and what does it mean?

4. How many oxygen atoms are reactants?

5. How many oxygen atoms are products?

6. CH4 2O2

7. CO2 2H2O

8. Subscript, there are 4 Hydrogen atoms

9. 4

10. 4

LAW OF CONSERVATION OF MASS

The mass of the products of a chemical reaction must be the same as the mass of the reactants in that reaction.

The number and kind of atoms must be equal on both sides of the equation.

Atoms are never lost or created in a chemical reaction; however, they do change partners.

ENERGY REACTIONS

Exothermic VS

Endothermic

EXOTHERMIC REACTIONS

Therm refers to heat energy Exo refers to out Exothermic reaction

a reaction in which energy is released during the reaction. The products have less energy than the reactants.

Exothermic reactions feel warmEnergy is written on the product side of the

equation.

ENDOTHERMIC REACTIONS

Endo refers to in Reaction in which energy is absorbed during

the reaction. The products have more energy than the reactants.

Endothermic reactions feel cold Energy is written on the reactant side of the

equation.