Objectives:Describe how chemical reactions produce new substances with different properties. Identify four signs that a chemical reaction might be taking place. Explain what happens to chemical bonds during a chemical reaction.

Chemical Reaction process of a substance completely changing to a different substance with different properties.

Clues of a chemical reaction 1. color change 2. gas formation 3. solid formation called a precipitate 4. energy given off as light, thermal, or electrical energy.

Chemical reactions happen when molecules bump into each other causing the starting bonds to break apart, the atoms rearrange, and new bonds are formed

Example: CH 4 + O 2 → CO 2 + H 2 O

Objectives: Interpret and write simple chemical formulas. Write and balance simple chemical equations. Explain how a balanced equation shows the law of conservation of mass

Chemical Symbol Shorter way to write an element’s name.

Chemical Formula combination of chemical symbols and numbers to represent a substance. It an easier way to write a molecules and compounds.

A chemical formula shows the number of atoms of each element in a molecule

Examples: H 2 O SO 4 Ca(OH) 2

Chemical formulas use subscripts and coefficients to show the number of atoms and molecules.

Subscript the small # to the right of the element that tells the # of atoms:

Examples: H 2 O SO 4 Ca(OH) 2

Coefficients large # to the left of the element. Applies to the whole molecule!

EXAMPLES 2H 2 O 4SO 4 3Ca(OH) 2

Writing Formulas for Covalent Compounds You can use the name of a covalent compound to write its chemical formula. The names of covalent compounds use prefixes. Each prefix represents a number, as shown below. mono-1hexa-6 di-2hepta - 7 tri-3octa-8 tetra-4nona-9 penta-5deca-10

How to Write Formulas for Covalent Compounds 1. name the first element 2. add a prefix if it has a subscript 3. name the second element 4. Add a prefix 5. Change ending of second element to “ ide ”

Let’s try some practice 1.CO 2 2.CO 3.SO 2 4.SO 3 5.N 2 O 6.N 2 O 3 7.NO 8.CCl 4 9.SiO 2 1.Carbon dioxide 2.Carbon monoxide 3.Sulfur dioxide 4.Sulfur trioxide 5.Dinitrogen monoxide 6.Dinitrogen trioxide 7.Nitrogen monoxide 8.Carbon tetrachloride 9.Silicon dioxide

Exceptions Some important exceptions to this naming scheme occur because the compounds were originally named before the methodical naming scheme above became widespread. Now a days, these names are so common that they're officially recognized: H2O is "water" PO4 is “phosphate” NH3 is "ammonia" CLO3 is “chlorate” CH4 is "methane“NO3 is “nitrate” SO4 is “Sulfate” CO3 is “carbonate” OH is “hydroxide”

Ionic Compounds To write the formula for an ionic compound, make sure the compound’s charge is 0. No prefixes…ends in ide

Chemical Equation an easier and shorter way to write a chemical reaction using chemical symbols and formulas as a shortcut to describe a chemical reaction

Example: CH 4 + O 2 → CO 2 + H 2 O

Reactants what you start with Products what you end with CH 4 + O 2 → CO 2 + H 2 O ReactantsProducts

Law of conservation of Mass states that mass can not be created or destroyed

An equation is balanced when the # of atoms in the reactants are = to the # of atoms in the products

You balance an equation by changing the coefficients, not the subscript!

Steps to balancing a chemical equation: 1. Write the unbalanced equation on your paper. 2. Draw a small line in front of each molecule. 3. Draw boxes around all the chemical formulas.

4. Make an element inventory. 5. Write numbers in front of each of the boxes until the inventory for each element is the same both before and after the reaction

Example __ Fe + __S → __FeS Element BeforeAfter Fe = ____ _____ S = ____ _____

__H 2 + __O 2 → __H 2 O Element BeforeAfter H = ____ _____ O = ____ _____

__Mg + __O 2 → __MgO Element BeforeAfter Mg = ____ _____ O = ____ _____

_Ca + _H 2 O → _Ca(OH) 2 + _H 2 Element BeforeAfter H = ____ _____ O = ____ _____ Ca = ____ _____