2/4/2014 What is the law of conservation of mass? What does it mean for a chemical reaction to be balanced?

I can balance a chemical reaction. Today’s Goal: I can balance a chemical reaction.

Today’s Plan: Review homework 2. Practice 3. Practice 4. Practice

H2O2 H2O + O2 Balancing Equations We know that matter cannot be created or destroyed – only changed from type to type We CANNOT change subscripts (the little number) – that will change the substance H2O2 H2O + O2

Today’s Goal: (H2O2)

So how can we make it balanced? H2O2 H2O + O2 H – 2 O -2 H – 2 O - 3 Right now, we cannot use the atoms from H2O2 to make H2O and O2 NOT O2 H H O O

2H2O2 2H2O + O2 We use coefficients. A coefficient is a big number that goes in front of an entire molecule and multiplies the entire molecule 2H2O2 2H2O + O2 H- 4 O - 4 H- 4 O – 2 + 2 = 4

2H2O2 2H2O + O2 H H O O H H O O

How many of each atom? 3Mg 5NaCl 2H2O 3H2SO4 2NaC2H3O2 Al(OH)3 2Ca(NO3)2 Mg - 3 Na – 5, Cl - 5 H – 4, O - 2 H – 6, S – 3, O – 12 Na – 2, C – 4, H – 6, O – 4 Al – 1, O – 3, H – 3 Ca – 2, N – 4, O - 12

Balancing Act Atoms are not created or destroyed during a chemical reaction. Scientists know that there must be the same number of atoms on each side of the arrow. To balance the chemical equation, you must add coefficients in front of the chemical formulas in the equations. You cannot change or remove subscripts!

To balance a chemical equation: Determine the number of atoms for each element. Mg + O2 MgO Mg – 1 O – 2 Mg – 1 O – 1

To balance a chemical equation: 2) Pick an element that is not equal on both sides of the equation. Mg + O2 MgO Mg – 1 O – 2 Mg – 1 O – 1

To balance a chemical equation: 3) Add a coefficient in front of the formula with that element and adjust your counts. Mg + O2 2 MgO Mg – 1 O – 2 Mg – 1 2 O – 1 2

To balance a chemical equation: 4) Continue adding coefficients to get the same number of atoms of each element of each side. 2 Mg + O2 2 MgO Mg – 1 2 O – 2 Mg – 1 2 O – 1 2

Ca + O2 CaO Ca – 1 O – 2 Ca – 1 O – 1

Ca + O2 2CaO Ca – 1 O – 2 Ca – 1 2 O – 1 2

2Ca + O2 2CaO Ca – 1 2 O – 2 Ca – 1 2 O – 1 2

N2 + H2 NH3 N – 2 H – 2 N – 1 H – 3

N2 + H2 2NH3 N – 2 H – 2 N – 1 2 H – 3 6

N2 + 3H2 2NH3 N – 2 H – 2 6 N – 1 2 H – 3 6

Cu2O + C Cu + CO2 Cu – 2 O – 1 C – 1 Cu – 1 O – 2 C – 1

2Cu2O + C Cu + CO2 Cu – 2 4 O – 1 2 C – 1 Cu – 1 O – 2 C – 1

2Cu2O + C 4Cu + CO2 Cu – 2 4 O – 1 2 C – 1 Cu – 1 4 O – 2 C – 1

H2O2 H2O + O2 H – 2 O – 2 H – 2 O – 3

H2O2 2H2O + O2 H – 2 O – 2 H – 2 4 O – 3 4

2H2O2 2H2O + O2 H – 2 4 O – 2 4 H – 2 4 O – 3 4