Chemical Equations

What is a “chemical equation”?  Chemical Equations use symbols to represent a chemical reaction and show the relationship between reactants and products of a reaction

More Simply…  They show what goes into a reaction and what comes out.

Examples  6 CO H 2 O → C 6 H 12 O O 2  Photosynthesis  2H 2 + O 2 → 2H 2 O  Production of Water  CH O 2 → CO H 2 O  Burning of a natural gas

Parts of a chemical equation  Lets look at the example for the production of water.  2H 2 + O 2 → 2H 2 O What elements or compounds are reacting? What elements or compounds are produced?

 2H 2 + O 2 → 2H 2 O  For this example:  Hydrogen is reacting with Oxygen  H 2 O or water is being produced

 What is reacting is known as the reactants.  Reactants are what the yield arrow is not facing towards.

 What is being produced is known as the product(s).  The yield arrow always points to the product(s).

Predict the reactants and products in the following equations.  2 AgI + Na 2 S → Ag 2 S + 2 NaI  4 FeS + 7 O 2 → 2 Fe 2 O SO 2  PCl H 2 O → H 3 PO HCl  SnO H 2 → Sn + 2 H 2 O

Coefficients vs Subscripts 2 H 2 + O 2  2H 2 O Coefficients Subscripts

What’s the difference between subscripts and coefficients?  Subscripts represent the number of atoms in a molecule.  Coefficients represent the number of moles.

 2 H 2 + O 2  2H 2 O Lets look at the first “2H 2 ” The first two in front of the H is called what? The small two to the right of the H is called what?

 2 H 2 The subscripts says that there are 2 Hydrogen atoms bonded together HH

 2 H 2 The coefficient states that there are 2 moles of H 2 HH HH

Mole-Mole Ratio  The mole-mole ratio states how many moles of a substance there is compared to another  Example N H 2 ---> 2 NH 3 What is the mole-mole ratio of N 2 to NH 3 ?

 N H 2 ---> 2 NH 3 The ratio of N 2 to NH 3 is: 1: 2 The ratio is directly related to the coefficient

 8 H 2 + S 8 ---> 8 H 2 S,  What is the mole-mole ratio of H 2 to S 8 ?

8 H 2 + S 8 ---> 8 H 2 S,  8:1  What about the ratio of H 2 to H 2 S?  8:8  But this can be reduced. The ratio should be 1:1

2 C 4 H O 2 ---> 8 CO H 2 O,  What is the ratio of:  C 4 H 10 / O 2  O 2 / CO 2  O 2 / H 2 O  C 4 H 10 / CO 2  C 4 H 10 / H 2 O Don’t forget to reduce your answers!

Balancing Equations  Equations are balanced when there are the same number of atoms on each side the equation. Law of conservation of mass: mass of reactants = mass of products

 In any chemical reaction  The mass of the reactants needs to equal the mass of the products  The total number of atoms on each side of the yield sign is the same

When balancing equations,  We can only change coefficients, not subscripts.  We change coefficients until the number of atoms is the same on both sides of the equation.

Practice  H 2 + O 2  H 2 O  Count the atoms on the reactant side  Count the atoms on the product side

H 2 + O 2  H 2 O  Reactants  H 2 = 2 H’s  O 2 = 2 O’s  Products  H 2 = 2 H’s  O = 1 O What’s not balanced?

Next: Add coefficients to make them balanced.  H 2 + O 2  2H 2 O  Gives me the correct amount of O’s but now I have 4 H’s  So what do I need to do?

 2H 2 + O 2  2H 2 O  Now I have the same amount of atoms on the reactant side as the product side.  This equation is now balanced.