1. Putting chemical reactions into words
Chemical Equations
Putting chemical reactions into words

2. A chemical equation is a symbolic representation of a chemical reaction.
Reactants  Products
Reactants yield products
Reactants produce products

3. The burning of methane gas in oxygen is:
Equation Example:
The burning of methane gas in oxygen is:
CH4 + 2 O2 → CO2 + 2 H2O

4. Review: Element Symbols
All elements are represented by a 1 or 2 letter symbol
For example
C = Carbon
Ne = Neon
O = Oxygen
The first letter is capitalized, the second is not

5. Chemical Formulas
Shows the elements & number of atoms of each element in a molecule/compound
H2SO4
Elements
Hydrogen; 2 atoms
Sulfur: 1 atom
Oxygen: 4 atoms
7 atoms total
The subscript describes the number of atoms of an element
If there is not a subscript listed, it is understood to be 1.
Subscript

6. Coefficients A formula may begin with a number.
If there is no number, then “1” is understood to be in front of the formula.
This number is called the coefficient.
The coefficient represents the number of molecules of that compound or atom needed in the reaction.
For example:
2H2SO4 – 2 molecules of Sulfuric Acid

7. 2H2SO4 – 2 molecules of Sulfuric Acid
A coefficient is distributed to ALL elements in a compound
2 – H2 (for a total of 4 H atoms)
2 – S (for a total of 2 S atoms)
2 – O4 (for a total of 8 O atoms)

8. Reading Chemical Equations
Each side of an equation represents a combination of chemicals.
The combination is written as a set of chemical formulas, separated by + symbols.
CH4 + 2 O2 → CO2 + 2 H2O

9. Reading Chemical Equations
The two sides of the equation are separated by an arrow.
Reactants: The combination of chemicals before the reaction are on the left side of the arrow
Products: The right side indicates the combination of chemicals after the reaction.

10. For Example:
4Na + O2 → 2Na2O
In this reaction, sodium (Na) and oxygen (O2) react to make a single molecule, Na2O
Label: Reactants, products, subscripts, coefficients

11. Atom Counts List the element symbols present (under the arrow).
Count the number of atoms for EACH element on the reactants side and also on the products side.
If both sides are equal for EVERY element, the equation is balanced.

12. List all element symbols and the number of atoms of each
Na + Cl  NaCl
Is it balanced?

13. List the element symbols and the number of atoms of each
2K + Cl  2KCl
Is it balanced?

14. Chemical Equations and Heat
Exothermic Reactions – chemical equations that produce heat. Heat is a product.
Endothermic Reactions – chemical equations that use heat. Heat is a reactant.