Chemical Reactions

How do you know that a chemical reaction has occurred? Physical Observations Color change Precipitate Heat Bubbles Smell

3CO(g) + Fe2O3(s)  2Fe(s) + 3CO2(g) Chemical Equation REACTANTS PRODUCTS 3CO(g) + Fe2O3(s)  2Fe(s) + 3CO2(g) ↑ # OF COMPOUNDS ↑ # OF ATOMS IN THE COMPOUND ↑ STATE SYMBOL

Balancing Chemical Equations Law of Conservation: Mass is neither created nor destroyed in an ordinary chemical or physical process Law of Conservation of Mass = Balanced Equations Same number of elements on both sides of equation

Balancing Chemical Equations Use coefficients in front of the compound to balance. NEVER change the subscripts, though you need to use them to balance the equation. Always use whole #’s 3CO(g) + Fe2O3(s)  2Fe(s) + 3CO2(g) 3 carbons 3 carbons 6 oxygen 6 oxygen 2 iron 2 Iron

Practice 2 KNO3  KNO2 + O2 2 CaC2 + O2  Ca + CO2 2 2

Writing Chemical Equations Start with the Reactants End with the Products An arrow separates to reactants and products Use a ‘+’ to separate one or more reactants or products Balance the equation If the equation does not balance, check your formulas

Writing Chemical Reactions Apply the physical state symbol to each compound Solid = s Liquid = l Gas = g Aqueous = aq Is a solid dissolved in water Know Diatomic elements, elements that are paired when not in a compound Br2 I2 N2 Cl2 H2 O2 F2

aluminum reacts with iodine to form aluminum iodide Practice zinc reacts with iron (III) chloride to form iron and zinc (II) chloride 3 Zn + 2 FeCl3 2 Fe + 3 ZnCl2 aluminum reacts with iodine to form aluminum iodide 2 Al + 3 I2  2 AlI3