Describing Chemical Reactions Chapter 6 Section 2

Chemical Formulas Let’s remember what chemical formulas are and what all of the letters and symbols mean. . .

Chemical Equations Short and easy way to show a reaction! Chemical formulas and symbols to summarize a reaction. Reactant + Reactant  Product + Product

Let’s Review… What are 4 types of evidence that a chemical reaction has occurred?

Conservation of Matter In a chemical reaction, the total mass of the reactants must equal the total mass of the products. The number of atoms will stay the same!

Open v. Closed System Open System Matter can enter from or escape to the surroundings Closed System Matter is not allowed to enter or leave

Balancing Chemical Equations A chemical equation MUST show the same number of each type of atom on both sides of the equation. H2 + O2  H2O Count your atoms! Count your atoms again! Is the equation balanced? # of hydrogen atoms on the reactant side: # of oxygen atoms on the reactant side: # of hydrogen atoms on the products side: # of oxygen atoms on the products side:

H2 + O2  H2O

Let’s Practice! Sn + Cl2  SnCl2 Sn: Cl:

Let’s Practice! Na + O2  Na2O Na: O: Na + O2  Na2O

Let’s Practice! Na + MgF2  NaF + Mg Na + MgF2  NaF + Mg Na: Mg: F: Download and open the document from Moodle called “Chemical Equations” Na + MgF2  NaF + Mg Na: Mg: F: Na + MgF2  NaF + Mg

Steps for Balancing Equations Synthesis Two or more elements or compounds combine to make a more complex substance. Decomposition Compounds break down into simpler products. Replacement One element replaces another in a compound or two elements trade places.

Steps for Balancing Equations Write the equation Count the atoms on both the reactant and product side Use Coefficients to Balance the Atoms Look back and Check your work.