Do Now for Wednesday, January 8th!

• Think! Think! Think!!!!• Explain how a simple chemical reaction might

save lives.

Another Chemical Reaction Saves Lives!

• Without Airbag With Airbag

The Chemistry Behind Airbags• Chemical Reactions Are Used to Generate the Gas Inside

an Airbag.• Airbags have been commonly available since the late

1980's; however, they were first invented (and a version was patented) in 1953. The automobile industry started in the late 1950's to research airbags and soon discovered that there were many more difficulties in the development of an airbag than anyone had expected. Crash tests showed that for an airbag to be useful as a protective device, the bag must deploy and inflate within 40 milliseconds.

The Chemistry Behind Airbags• The instant a collision happens, a pellet of sodium azide

(NaN3) is ignited. A rapid chemical reaction occurs, generating nitrogen gas (N2). This gas fills a nylon bag at a velocity of 150 to 250 miles per hour. This process, from the initial impact of the crash to full inflation of the airbags, takes only about 40 milliseconds. Ideally, the body of the driver (or passenger) should not hit the airbag while it is still inflating.

“Do Now” for Friday, January 10

• There are three basic types of chemical reactions. List and give an example of each.

Chemical Reactions and Equations

What is a chemical equation?

A chemical equation is a shorter, easier way to show chemical reactions, using symbols instead of words.

5 Ways to know that a chemical reaction has occurred:1. Color Change2. Heat Produced-Gets Warm (exothermic)3. Heat Absorbed-Gets Cold (endothermic)4. Gas Produced (fizzzzz)5. Solid Produced (precipitate)These are indications of CHEMICAL CHANGES

Physical Changes do not tell you a chemical reaction has occurred!

Physical change = phase changes from solidliquidgasChanges in shape

Is a chemical reaction occurring?

Is a chemical reaction occurring?

Is a chemical reaction occurring?

Is a chemical reaction occurring?

Is a chemical reaction occurring?

Is a chemical reaction occurring?

Is a chemical reaction occurring?

Is a chemical reaction occurring?

Chemical formulas…

• Are the “words” in the language of chemistry

In the last unit you learned how to name compounds and write their formulas. You learned some formula “words” like:

Carbon Monoxide Carbon Dioxide Water Hydrogen Peroxide

CO CO2 H2O H2O2

Chemical Equations are the “sentences” in the language of chemistry. Chemistry students put the “words” (formulas) together to make “sentences” (chemical equations)Every chemical equation has formulas as well as special symbols.

Basic rules for chemical equations1. Chemical equations read from left to right.2. Each equation has two halves divided by an arrow. The half left of the arrow is the REACTANT side and the half right of the arrow is the PRODUCT side.

So what do the numbers mean?

We use SUBSCRIPTS to show the number of atoms of different elements in a formula.

We use COEFFICIENTS to balance an equation. Coefficients are numbers placed in front of a chemical formula in an equation and tell you how many atoms or molecules of each reactant and product are involved in the reaction.

RULES OF CHEMICAL EQUATIONS:

1. The Law of Conservation of Mass states that chemical equations must start and end with the same number of atoms of each substance on both sides of the arrow. We call this a BALANCED chemical equation!

All chemical reactions must be balanced. This means that the number of atoms on the reactant side must be equal to the number of atoms on the product side.

2. To balance the equation, you can ONLY change the coefficients, NOT the subscripts!(e.g., changing CO2 to 3CO2 is OK. Changing CO2 to CO4 is not.)

3. To calculate the number of atoms for each atom, you MULTIPLY the coefficient times the subscripts (e.g., 3 CO2 = 3 Carbons and 6 Oxygens)

4. You MUST have only integer coefficients when you are finished, no decimals, no fractions! (e.g., 6.5 O2 is not ok, 13 O2 is ok)

5. You MUST have the lowest possible integer coefficients when you are finished.

UNBALANCED

BALANCED!

Three Types of Chemical Reactions

Demonstrated by the Flintstones!

Synthesis – When two or more elements or compounds combine

to make a more complex substance.

2H2 + O2 2H2OSynthesis of Water

Decomposition – Occurs when compounds break down into simpler

products.

2H2O2 2H2O + O2Decomposition of Hydrogen Peroxide

Replacement – When one element replaces another in a compound.

2Cu2O + C 4 Cu + CO2Replacement of Oxygen in Copper Oxide

Practice!