Presentation on theme: "Balancing Chemical Equations"— Presentation transcript:
1 Balancing Chemical Equations What goes in must come out!
2 What is the Law of Conservation of Mass? In the reaction N2 + 3H2 2NH3If 14 grams of N2 reacted with 3 grams of H2, how many grams of ammonia would be produced?
3 Law of Conservation of Mass You need to remember this law! The Law of Conservation of Mass states: that mass is neither created nor destroyed in any chemical reaction. Therefore balancing of equations requires the same number of atoms on both sides of a chemical reaction.The number of atoms in the Reactants must equal the Number of atoms in the Products
4 Do these reactions abide by the Law of Conservation of Mass? YES!
5 Balancing Chemical Equations Balancing a chemical equation is much like the work of an accountant who has to show every penny that comes in and where it has gone to.
6 In order to balance equations, we first must remember…. How to count atoms!CO26CO2C atoms= 6O atoms= 6 x 2= 12C atoms= 1O atoms= 28Mg(NO3)2Mg atoms= 8N atoms= 8 x 1 x 2= 16O atoms= 8 x 3 x 2= 48
14 Mg + O2 MgO Mg + O2 MgO 2  Just count up the atoms on each side  The numbers aren’t balanced so then add “BIG” numbers to make up for any shortagesMg + O2 MgOMgO12222And adjust totals
15 WE SAY THAT THE EQUATION IS BALANCED!! But the numbers still aren’t equal, so add another “BIG” number2Mg + O2 MgOMgO122And adjust totals againNOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMSWE SAY THAT THE EQUATION IS BALANCED!!
16 Try to balance these equations on WS D. 6(p Try to balance these equations on WS D.6(p.4 of your packet) using the same method: H2 + O2 H2O Mg + O2 MgO Ca + H2O Ca(OH)2 + H2
17 Try to balance these equations on WS D. 6(p Try to balance these equations on WS D.6(p.4 of your packet) using the same method: 2H2 + O2 2H2O 2Mg + O2 2MgO Ca + 2H2O Ca(OH)2 + H2
19 Steps to Balance Equations: Balance elements that appear only once on each side of the arrow.Next balance elements that appear only once on each side but have different numbers of atoms.Finally balance elements that are in two formulas in the same side.
20 Example NH3 + O2 NO + H2O Reactants Products N appears once on both sides in equal numbers, so the coefficient for NH3 is the same as for NO.
21 Example: NH3 + O NO + H2ONext look at H which appears only once on each side but has different numbers of atoms, 3 on the left and 2 on the right. The least common multiple of 3 and 2 is 6, so rewrite the equation to get 6 atoms of H on both sides:2NH3 + O NO + 3H2O
22 Example: 2NH3 + O NO + 3H2OThere are 2 oxygen atoms on the left and 5 on the right — the least common multiple of 2 and 5 is 10, so rewrite the equation as:2NH3 + 5O NO + 6H2O
23 Now count the atoms on each side: 2NH3 + 5O NO + 6H2OWrite them out keeping them on the appropriate side of the chemical equation2 N (nitrogen atoms) N (nitrogen atoms)6 H (hydrogen atoms) H (hydrogen atoms)10 O (oxygen atoms) O (oxygen atoms)This shows the equation not to be balanced “YET”
24 Check the number again: If you double the N and H on the left the equation will be balanced:4NH3 + 5O NO + 6H2O
25 Double-check: 4NH3 + 5O2 4NO + 6H2O The equation is Balanced 4 N (nitrogen atoms) 4 N (nitrogen atoms)12 H (hydrogen atoms) 12 H (hydrogen atoms)10 O (oxygen atoms) 10 O (oxygen atoms)The equation is Balanced