1 “Chemical Reactions”

2 Describing Chemical Reactions l OBJECTIVES: –Describe how to write a word equation. –Describe how to write a chemical equation.

3 Chemical Reactions _____________________________________ Examples – H 2 + O 2  H 2 O CH 4 + O 2  CO 2 + H 2 O

4 All chemical reactions… l have two parts: 1.Reactants = _______________ 2.Products = _______________ l The reactants will turn into the products. Reactants  Products

5 If it were math… l have two parts: 1.Reactants = _______________ 2.Products = _______________ l The reactants will turn into the products. Reactants  Products

6 In a chemical reaction l A reaction can be described several ways: 1) _______________ a of describing a chemical reaction using the names of the reactants and products e.g. Iron + sulfur  iron (II) sulfide + energy 2) _______________ a of way describing a chemical reaction using the chemical formula of the reactants and products e.g. Fe + S  FeS

7 Symbols in equations? l the arrow (→) separates the reactants from the products (arrow points to products) –Read as: “reacts to form” or yields l The plus sign (+) = “and” meaning that they are in contact with each other

8 Symbols Con’t _______________ Includes a description of the state of the reactants and products l (s) after the formula = solid: Fe (s) l (g) after the formula = gas: CO 2(g) l (l) after the formula = liquid: H 2 O (l) l (aq) after the formula = dissolved in water, an aqueous solution: NaCl (aq) is a salt water solution e.g. Zn (s) + CuSO 4(aq)  ZnSO 4(aq) + Cu (s)

9 Energy l Energy can either be absorbed or released and is only written in a chemical equation l _______________ e.g. Zn (s) + CuSO 4(aq)  ZnSO 4(aq) + Cu (s) Energy l _______________ e.g. Energy + CuCO 3(s)  CO 2(g) + CuO (s)

10 Energy l If Energy is absorbed it is taken from the environment  ________ l If Energy is released it is sent into the environment  ________

11 Write a chemical equation for: 1. Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride, hydrogen sulfide gas and energy. _______________ 2. Using energy, sodium chloride dissolves in water to form aqueous Sodium and Chloride Ions. _______________

12 Write a sentence for the following then write it as a word equation: Energy + Fe (s) + O 2(g)  Fe 2 O 3(s) _______________ **states are not included in word equations**

13 What is a catalyst? l A substance that speeds up a reaction, without being changed or used up by the reaction. l __________ are biological or protein catalysts in your body.