CHEMICAL REACTIONS & EQUATIONS

Chemical Reactions

Chemical Reactions Process in which one or more substances are converted into new substances with different physical and chemical properties For example, a yellow solid precipitate, lead iodide (PbI2), forms from the mixture of two clear liquids, potassium iodide (KI) and lead nitrate (Pb(NO3)2).

Word Equation Hydrogen + Oxygen Water + Energy Reactants Products

Classification of Chemical Reactions 1. Synthesis 2. Decomposition 3. Single Replacement 4. Combustion (burning)

A B AB Synthesis Examples: 1 2 Cu + O2 CuO 1 H2CO3 CO2 + H2O Two reactants combine to form a single product (compound). A B AB One Product Examples: 1 2 Cu + O2 CuO 1 H2CO3 CO2 + H2O

AB A B Decomposition Examples: 2 3 KClO3 KCl + O2 1 2 H2O2 H2O + O2 One reactant breaks down to form two or more products. AB A B One Reactant Examples: 2 3 KClO3 KCl + O2 1 2 H2O2 H2O + O2

A BC AC B Single Replacement Examples: 2 1 Mg + HCl MgCl2 + H2 2 1 One element replaces another from a compound A BC AC B Examples: 2 1 Mg + HCl MgCl2 + H2 2 1 Cl2 + KI KCl + I2

Combustion (burning) CxHy+ O2 CO2 + H2O C3H8 + O2 CO2 + H2O C2H2+ O2 Produces light and heat CxHy+ O2 CO2 + H2O Balance C 1st, then H, then O (because it splits up) 4 1 C3H8 + O2 5 CO2 + H2O 3 1 2 2.5 5 2 4 2 1 C2H2+ O2 CO2 + H2O

Classification of Equations SYNTHESIS AB A B Ca S CaS DECOMPOSITION AB A B 2HgO 2Hg O2

Classification of Equations SINGLE REPLACEMENT BC AB C A 2KCl Br2 Cl2 2KBr

Rules for Balancing Equations 1. Obey the LAW OF CONSERVATION OF MASS. Same number of each kind of atom on both sides of the equation. 25g + 25g + 50 g 50 g + 150 g ?g

How to Balance an Equation 2. To balance atoms of reactants and products, change ONLY the coefficients. 3. Do NOT change the chemical formula to balance numbers of atoms. Numbers IN FRONT of the formulas NOTE: Subscripts are lower numbers in formula 4 Al2O3 Coefficient Subscripts

How to Balance an Equation cont. 4. Check your work by counting atoms of each element. 6. Check to see that the coefficients are in the lowest whole number ratio. 2H2O (l) 2H2 (g) + 1O2 (g) 4 Hydrogen 4 Hydrogen 2 Oxygen 2 Oxygen

Practice Balancing These Equations Ca + O2 CaO 2 1 2 1 Ca 1 Ca 2 O 1 O *Hint: Start by making the uneven side even. 2 O 2 O 1 Ca 2 Ca 2 Ca 2 Ca 2 O 2 O 2 Ca, 2 O 2 Ca, 2 O

Practice 1 2 1 2 CH4 + O2 CO2 + H2O 2 O 3 O 4 O 4 O 1 C 1 C 4 H 4 H *Hint: Start with the element that is split up: Oxygen. Then, make uneven side even. 2 O 3 O 4 O 4 O 1 C 1 C 4 H 4 H 1 C, 4 H, 4 O 1 C, 4 H, 4 O

Practice Fe + Cl2 FeCl3 2 1 3 2 1 Fe 1 Fe 2 Cl 3 Cl 6 Cl 6 Cl 1 Fe 2 Fe 2 Fe 2 Fe 2 Fe, 6 Cl2 2 Fe, 6 Cl2

Practice 2 HgO Hg + O2 2 1 1 3 2 Al + MnO Al2O3 + Mn 3 2 Al, 3 Mn, 3 O Br2+ NaI NaBr + I2 1 2 2 Br, 2 Na, 2 I 2 Br, 2 Na, 2 I Do these on own 2 HgO Hg + O2 2 1 2 Hg, 2 O 2 Hg, 2 O