chemical equations

CHEMISTRY II

UNIT IChemical Equations. The language of

reactions

CHEMISTRY

The branch of science that deals with the characteristics and composition of all materials and with the reactions they can undergo

The Chemistry and its relation with other sciences.

BIOLOGY

PHYSICS

MATHEMATICS

SOCIAL SCIENCES

Physical Changes

Physical changes are about energy and states of matter changes.

A physical change does not produce a new substance. Changes in state or phase (melting, freezing, vaporization, condensation, sublimation) are physical changes.

Examples of physical changes include crushing a can, melting an ice cube, and breaking a bottle.

Physical properties

Are characteristics that describe a physical change

State of matter (solid, liquid, gas) Boiling point, melting point Density Color, Odor, hardness. Malleability (a metal able to extend in wires). Ductibility (a metal able to extend in foils or

sheets).

Chemical changes

Chemical changes take place on the molecular level.

A chemical change produces a new substance.

Examples of chemical changes include combustion (burning), cooking an egg, rusting of an iron pan, and mixing hydrochloric acid and sodium hydroxide to make salt and water

Chemical properties

Are characteristics that describe a physical change.

Flammability Reactivity (reacts with water, …) Combustion (process of burning) Oxidation Reduction

Chemical Formulas

Use the criss cross method using the oxidation numbers in each group

Write first the more mettallic (left periodic table) and then the least metallic (right of periodic table)

Na1+ Cl1- NaCl Al3+ O2- Al2O3

Chemical Equations

Reactants

Coefficient 2H2 + O2 2H2O

Subscript Products

Counting atoms (Activity #1 Portfolio)

Balancing Chemical Equations

Apply the Law of Conservation of Mass to get the same number of atoms of every element on each side of the equation. Tip: Start by balancing an element that appears in only once reactant and product.

Laws

Based on the Law of conservation of matter:

“Matter is not created nor destroyed, it is only transformed”

Thus

Law of Conservation of Mass is a relation stating that in a chemical reaction, the of the products equals the mass of the reactants.

1. Balance chemical formulas by placing coefficients in front of them to get the same number of atoms of every element on each side of the equation. DO NOT ADD SUBSCRIPTS, because this will change the formulas.

2. Start by balancing an element that appears in only one reactant and product.

3. Indicate the states of matter of the reactants and products

2H2 + O2 2H2O

Balance the following equations (Activity #2 Portfolio)

Fe + Cl2 FeCl3

Mg + O2 MgO

Cr2O7+ H2 Cr + H2O

CuSO4*5H2O CuSO4 + H2O

C4H10 + O2 H2O + CO2

KMnO4 + HCl KCl + MnCl2 + H2O + Cl2