Chemical Equations and Chemical Reactions http://www.personal.kent.edu/~cearley/ChemWrld/balance/balance.htm

Writing A Chemical Equation The general format for chemical equations is: a + b  c + d The substances on the left side of the equation (a and b in this case) are called the reactant(s).

The + sign means “reacts with”. The  means “produces or yields”. The substance(s) on the right side of the equation (c and d in this case) are called the product(s).

Lets work with the statement Hydrogen gas reacts with oxygen gas to form liquid water.

Word Equation: hydrogen + oxygen  water Skeleton Equation: H2(g)+ O2(g)  H2O(l) Balanced Equation: ___H2(g)+ ___O2(g)  ___H2O(l) 2H2(g)+ O2(g)  2H2O(l)

Why must we balance equations? The Law of Conservation of Mass states that the total mass of reactants is always equal to the total mass of the products. (Lavoisier’s law) Antoine-Laurent Lavoisier experimenting to determine the composition of water, French engraving, 19th century. http://www.britannica.com/eb/art-15464/Antoine-Laurent-Lavoisier-experimenting-to-determine-the-composition-of-water

Why must we balance equations? Dalton’s atomic theory states that atoms can not be created or destroyed. Compounds are formed when atoms of different elements combine in fixed proportions. John Dalton, F.R.S., engraved by Worthington after an 1814 painting by William Allen, published 25 June 1823 in Manchester and London. Note the charts with Dalton's atomic symbols lying on the table. Fisher Collection, Chemical Heritage Foundation.

To balance equations numbers called coefficients are put before the formulas. This changes the number of molecules. You cannot add or change subscripts (small numbers). You do not write coefficients of 1 (one). Sometimes you need to know the state of the chemicals that are involved in a chemical reaction.

State Abbreviation solid liquid gas aqueous solution

State Abbreviation solid (s) liquid gas aqueous solution

State Abbreviation solid (s) liquid (l) gas aqueous solution

State Abbreviation solid (s) liquid (l) gas (g) aqueous solution

State Abbreviation solid (s) liquid (l) gas (g) aqueous solution (aq)

Rules For Writing Balanced Chemical Equations Final Balanced Chemical Equation 2H2(g) + O2(g)  2H2O(l) Rules For Writing Balanced Chemical Equations This requires a lot of practice and patience. These rules will not apply in all equations. 1. Write the skeleton equation.

Look for a polyatomic ion that appears once on each side of the equation. Balance these first. Pick single elements that appears on each side. Choose coefficients to balance this element. The terms you balanced in the previous step have to remain balanced. Repeat for any other elements.

4. Check for any term you have not yet looked at 4. Check for any term you have not yet looked at. Adjust the coefficient of the term so that the numbers of the elements appearing in that term are balanced across the whole equation. If you have any fraction coefficients clear them by multiplying. Also, make sure you have the smallest possible coefficients by reducing. 5. Check the equation!

Example 1 Word Equation: Skeletal Equation: Na + H2O  NaOH + H2(g) sodium + water  sodium hydroxide + hydrogen gas Skeletal Equation: Na + H2O  NaOH + H2(g) Balanced Equation: ___Na + ___H2O  ___NaOH +___H2(g) 2Na + 2H2O  2NaOH + H2(g)

Example 2 Balanced Chemical Equation 2H2O__ 2Na__ +  2NaOH__ + H2___ 2H2O(l) + 2 Na(s)  2NaOH(aq) + H2(g) Verification Reactants Products 2 Na atoms 4 H atoms 2 O atoms

Example 2 Word Equation: Skeletal Equation: copper + silver nitrate  copper(II) nitrate + silver Skeletal Equation: ___ + ______  ______ + ___ Cu + AgNO3  Cu(NO3)2 + Ag

Example 2… Balanced Equation: __Cu +__ AgNO3  __Cu(NO3)2 + __Ag Balanced Chemical Equation: Cu__ + 2AgNO3__  Cu(NO3)2__ + 2Ag__ Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)

Reactants Products Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) Verification Reactants Products

Reactants Products 1 Cu atom Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) Verification Reactants Products 1 Cu atom

Reactants Products 1 Cu atom Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) Verification Reactants Products 1 Cu atom

Reactants Products 1 Cu atom 2 Ag atoms Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) Verification Reactants Products 1 Cu atom 2 Ag atoms

Reactants Products 1 Cu atom 2 Ag atoms Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) Verification Reactants Products 1 Cu atom 2 Ag atoms

Reactants Products 1 Cu atom 2 Ag atoms 2 NO3- ions Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) Verification Reactants Products 1 Cu atom 2 Ag atoms 2 NO3- ions

Reactants Products 1 Cu atom 2 Ag atoms 2 NO3- ions Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) Verification Reactants Products 1 Cu atom 2 Ag atoms 2 NO3- ions

Example 3 Word Equation: calcium nitrate + sodium hydroxide  calcium hydroxide + sodium nitrate Skeletal Equation: Ca(NO3)2 + NaOH  Ca(OH)2 + NaNO3 Balanced Equation: __Ca(NO3)2 + __NaOH  __Ca(OH)2 + _NaNO3 Ca(NO3)2 + 2NaOH  Ca(OH)2 + 2NaNO3

Balanced Chemical Equation Ca(NO3)2__ + 2NaOH__  Ca(OH)2__ + NaNO3__ Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + NaNO3(aq)

Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq) Reactants Products

Reactants Products 1 Ca atom Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq) Reactants Products 1 Ca atom

Reactants Products 1 Ca atom Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq) Reactants Products 1 Ca atom

Reactants Products 1 Ca atom 2 NO3- ions Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq) Reactants Products 1 Ca atom 2 NO3- ions

Reactants Products 1 Ca atom 2 NO3- ions Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq) Reactants Products 1 Ca atom 2 NO3- ions

Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq) Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms

Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq) Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms

Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms 2 OH- ions Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq) Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms 2 OH- ions

Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms 2 OH- ions Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq) Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms 2 OH- ions

http://www.ahajokes.com/cartoon/mathchem.gif Homework p. 174 # 1 to 6