CHAPTER 20CHAPTER 20

CHEMICAL REACTIONS

20.3 Conservation of Mass20.3 Conservation of Mass

Antoine Laurent __________ (1743-94), established an important principal based on his experiments with chemical reactions.

The total mass of the ________ of a reaction is equal to the total mass of the __________.

This is known as the law of ___________ of mass.

CONSERVATIONCONSERVATION OF MASS OF MASS

Total MASS of PRODUCTS EQUALS Total MASS of REACTANTS–Must MEASURE in a _________ SYSTEMAntoine Lavoisier

CONSERVATION OF CONSERVATION OF MASSMASS

Mass of WOOD and AIR before burning a fire

EQUALSMass of ASH and GASES after burning a fire

COOKING WITH COOKING WITH CHEMISTRYCHEMISTRY

CHEMICAL EQUATIONS ARE LIKE RECIPES

They tell you QUANTITIES of INGREDIENTS and Quantities of PRODUCTS

CHEMICAL EQUATIONSCHEMICAL EQUATIONS

NUMBER of REACTANT MOLECULES needed to MAKE a CERTAIN NUMBER of PRODUCT MOLECULES

2Na + Cl2 ----> 2NaCl

BALANCED BALANCED EQUATIONSEQUATIONS

Correct RATIOS of Molecules are shown as COEFFICIENTS in BALANCED EQUATIONS

2H2 + O2 ----> 2H2O

UNBALANCED UNBALANCED REACTIONSREACTIONS

REACTANTS ARE NOT ALWAYS PRESENT IN THE EXACT RATIOS NEEDED.

SO WHAT HAPPENS ?

_______ REACTANT The reactant molecule which is used up _____

_______ the AMOUNT of PRODUCT formed

UNBALANCED UNBALANCED REACTIONSREACTIONS

__________ REACTANT The reactant molecule which is _____ completely used up.

Some will be _____ _____ after reaction is complete.

UNBALANCED UNBALANCED REACTIONSREACTIONS

YIELDSYIELDS

REACTIONS DON’T ALWAYS TURN OUT AS PLANNED

HOW MUCH PRODUCT IS REALLY FORMED ?

_________ YIELD – The amount of Product ________ from the balanced equation

_________ YIELD – The amount of Product _________ formed

PERCENT YIELDPERCENT YIELD RATIO of Actual Yield to RATIO of Actual Yield to Predicted YieldPredicted Yield

%YIELD = %YIELD = Actual Yield Actual Yield x 100% x 100% Predicted YieldPredicted Yield

PERCENT YIELDPERCENT YIELD

IF we expect 100g. of product from chemical equation, BUT we only get 85g. of product, THEN

% YIELD = (85g./100g.)x100%

= 85%

20.4 Using Equations as 20.4 Using Equations as RecipesRecipes

Recipe #1: Chocolate Cake Recipe1 cup flour

1/2 cup cocoapowder

1/2 cup butter1 tsp vanilla1 cup sugar

1 teaspoon baking powder1/2 cup milk

1 egg

In a bowl, combine flour, sugar, cocoa powder, and baking power. Add butter, milk, vanilla, and egg. Mix until smooth. Bake in a 350°F oven for 35 minutes. Makes 8 servings

20.4 Using Equations as 20.4 Using Equations as RecipesRecipes

Recipe #2: Water

2 molecules of hydrogen gas1 molecule of oxygen gas

Combine the molecules in a closed container. Add a spark of electricity. Makes two molecules of water.

20.4 Using Equations as 20.4 Using Equations as RecipesRecipes

Balanced equations show how mass and atoms are conserved.

20.4 Using Equations as 20.4 Using Equations as RecipesRecipes

20.4 Using Equations20.4 Using Equations

Key Question:

How can you predict the amount of product in a reaction?

*Read text section 20.4 BEFORE Investigation 20.4