Chemical Equations and Formulas Test Review Subscripts give the correct ratio of _________? ATOMS A coefficient tells us the number of ________________ ? MOLECULES

Chemical Equations and Formulas Test Review 2C10H22 + O2 → CO2 + 22H2O is an example of___? A CHEMICAL EQUATION The left side of the equation shows the______ and the right side shows the ______. REACTANTS PRODUCTS The arrow in the middle of the equation separating the reactants and products is called the _________. YIELD SIGN

Chemical Equations and Formulas Test Review Why must chemical equations be balanced? BECAUSE THE LAW OF CONSERVATION OF MASS STATES THAT MATTER CAN NOT BE DESTROYED OR CREATED, ATOMS IN A REACTION ARE ONLY REARANGED TO FORM NEW SUBSTANCES What is the first step to balance an equation? COUNT THE NUMBER OF ATOMS FOR EACH ELEMENT ON BOTH SIDES OF THE EQUATION

Chemical Equations and Formulas Test Review What is done to fix an unbalanced equation? YOU CHANGE COEFFICIENTS AS NEEDED Can you change the subscript to balance an equation? Give an explanation why you can or can’t change subscripts. YOU CAN NEVER CHANGE A SUBSCRIPT TO BALANCE AN EQUATION. BECAUSE IF YOU CHANGE THE SUBSCRIPT, YOU ARE CHANGING THE SUBSTANCE. FOR EXAMPLE O2 IS ATMOSPHERIC OXYGEN AND O3 IS OZONE, 2 COMPLETELY DIFFERENT SUBSTANCES

Chemical Equations and Formulas Test Review Fe + 4H2O →Fe3O4 + 4H2 Count the Atoms for the equation. Fe= 1 Fe= 3 H= 8 H = 8 O= 4 O= 4 The equation is unbalanced, what changes do you make to balance this equation? ADD A 3 TO THE IRON (Fe) REACTANT SIDE 3Fe + 4H2O →Fe3O4 + 4H2

Chemical Equations and Formulas Test Review 2NCl3 → N2 + Cl2 Is this a balanced equation? Balance if needed. NO, YOU NEED TO ADD A COEFFICENT OF 3 IN FRONT OF CHLORINE. 2NCl3 → N2 + 3Cl2 H2O +SO3 → H2SO4 Is this a balanced equation? Balance if needed. YES THIS IS A BALNCED EQUATION H3BO3 + K → B + KOH Is this a balanced equation? Balance if needed NO, YOU NEED TO ADD A COEFFICENT OF 3 IN FRONT OF POTTASIUM ON BOTH SIDES OF THE EQUATION H3BO3 + 3K → B + 3KOH

Chemical Equations and Formulas Test Review C What is the chemical formula for the model ? CH4 H H H H

Chemical Equations and Formulas Test Review 1 2 3 Which model represents the formula NH2 ? MODEL NUMBER 3

Chemical Equations and Formulas Test Review What is the difference between a compound and molecule? A molecule is formed when two or more atoms join together chemically. A compound is a molecule that contains at least two different  elements. Elements are pure. Molecule Example--H2 Compound Example -- CaCo3 (also a molecule) CH4 + O2 CO2 + H2O Balance this equation CH4 + 2O2 CO2 + 2H2O

Chemical Equations and Formulas Test Review How many elements are in the compound 2H3PO4 THREE, HYDROGEN, PHOSPHORUS, AND OXYGEN How many molecules are present in the compound above? TWO MOLECULES OF H3PO4 C4H10 + O2 4CO2 + 5H2O How many molecules are produced from burning propane? 9, 4CO2 + 5H2O

Chemical Equations and Formulas Test Review 1 + + 2 + + 3 + + Which model best represents the law of conservation of mass? MODEL 3 – 6 ATOMS IN REACTION, 6 IN PRODUCT

Balance the following equations Fe + Cl2 FeCl3 2 Fe + 3 Cl2 2 FeCl3 N2 + H2 NH3 N2 + 3 H2 2 NH3 NaCl + F2 NaF + Cl2 2 NaCl + F2 2 NaF + Cl2

What will be different about a chemical change verses a physical change in looking at the chemical formula? In a physical change, the substance’s chemical formula does not change. Ex: Boiling water is still H2O but in vapor gas form. In a chemical change, the atoms and elements have rearranged to form new substances with new and different properties. Ex: Sodium, a reactive metal, reacts with Chlorine gas to yield NaCl, table salt.