1. Chemical Reactions: An Introduction Chapter 6

2. Pre-Chapter Questions 1.How can you tell that a chemical reaction has taken place? 2.What is the law of conservation of matter?

3. Signs of a chemical reaction

4. IMPORTANT CONCEPT! IN A CHEMICAL REACTION, ATOMS ARE NEITHER CREATED NOR DESTROYED. THERE MUST BE THE SAME NUMBER AND TYPE OF ATOMS ON BOTH THE REACTANT AND PRODUCT SIDES

5. Chemical Equations Chemical reactions involve a rearrangement of the ways atoms are grouped together. A chemical equation represents a chemical reaction. –Reactants are shown to the left of an arrow. –Products are shown to the right of the arrow.

6. Don’t forget the states! (of matter)

7. Diatomic Elements When these elements are by themselves they appear in pairs Nitrogen Hydrogen Oxygen Fluorine Chlorine Bromine Iodine

8. It’s all a balancing act

9. System for Balancing Chemical Reactions 1.Read the description of the chemical reaction, identifying the reactants and products as well as their phases. 2.Write the appropriate formula for each reactant and product. Remember that a correct formula for ionic compounds has subscripts that balance the charge of the compound. Also remember which elements occur naturally as diatomic molecules. 3.Write the unbalanced chemical equation that summarizes the chemical reaction. 4.Count the number of atoms of each element in the reactants and products. For simplicity, a polyatomic ion appearing unchanged on both sides of the equation is counted as a single unit. 5.Balance the elements one at a time by using coefficients. When no coefficient is written, it is assumed to be 1. You must not attempt to balance an equation by changing the subscripts in the chemical formula of a substance. 6.Check each atom or polyatomic ion to be sure that the equation is balanced. 7.Make sure all the coefficients are in their least whole number ratio.

10. Example Hydrogen gas and oxygen gas combine to form liquid water. Step 1: Identify the reactants and products Hydrogen gas and oxygen gas combine to form liquid water. Step 2 & 3: Write the unbalanced chemical equation H 2 (g) + O 2 (g) H 2 O(l)

11. Example continued H 2 (g) + O 2 (g) H 2 O(l) Step 4: Take the inventory 2 H 2 O Step 5: Balance by adding coefficients. Re-take inventory after each change to the equation Step 6 & 7: Check your answer. Make sure coeff. are in lowest whole number ratio. 2 H 1 O 2 4 2 2 4

12. Try a few more… 1.Solid iron(III) oxide reacts with aqueous nitric acid to from aqueous iron(III) nitrate and water. 2.Hydrosulfuric acid gas reacts with aqueous lead(II) nitrate to from solid lead(II) sulfide and aqueous nitric acid