Chemical Equations
General Chemistry
Jim Thorpe High School
Oh, no… Vocabulary!
• Coefficient:
is a small, whole number that appears IN FRONT
of a chemical formula in a chemical equation.
• Example: 4 HCl
• Word Equation:
an equation in which the reactants and products in a
chemical reaction are represented by words.
• Example: hydrogen + oxygen yields water
• Formula Equation:
represents the reactants and products of a chemical
reaction by their symbols or formulas.
• Example: 2 H2 + O2  2 H2O
Why are we learning this?
1.
The coefficients of a chemical reaction indicate
relative amounts of reactants and products.
Coefficients are MOLE RATIOS
Example: H2(g) + Cl2(g)  2HCl(g)
1 mol H2 : 1 mol Cl2 : 2 moles HCl
2.
The relative masses of the reactants and
products can also be determined from the
coefficients.
Example:
1 mol H2 = 2.02 g H2
1 mol Cl2 = 70.90 g Cl2
2 mol HCl = 72.92 g HCl
Therefore, 2.02g H2 will react with
70.90g Cl2 to form 72.92g of HCl.
3.
The reverse reaction for a chemical
equation has the same relative amounts of
substances as the forward reaction.
So what?
Because of this, chemical reactions can be
read in any direction. Forward and Reverse.
Ahh…not another note card!
Symbols used in Chemical Equations
• Open your books to page 246.
• Tonight cut out 13 flashcards.
• On the front of each card, draw the
symbol.
• On the back, write its explanation.
• When you are finished, find a
partner and practice!
Law of Conservation of
Mass
The law of conservation of mass states that
matter is neither lost nor gained in
chemical reactions. It simply changes
form.
Dalton’s
Law of Definite Proportions
Atoms are indestructible and
unchangeable, so compounds
are formed when one atom
chemically combines with other
atoms.
When elements react to form
compounds, they react in
defined, whole-number ratios.
Reactions are not random
events. They proceed
according to precise and welldefined formulas.
Rules for Balancing Equations
1. Write a word equation.
Determine the reactants,
the products, and the
physical states involved.
1. Solid zinc and
hydrochloric acid react to
yield zinc chloride and
hydrogen gas.
2. Translate to Chemistry.
Write the unbalanced
equation that summarizes
the reaction described in
Step 1, using chemical
formulas for names.
2. Zn(s) + HCl  ZnCl2 + H2(g)
Rules for Balancing Equations
3. Satisfy the law of
conservation of
mass.
Start with the most
complicated molecule.
Determine the
coefficients necessary
to satisfy the law of
conservation of mass.
3. Zn(s) + HCl  ZnCl2 + H2(g)
4. Check your work.
4. 1 Zn, 2 H, 2 Cl  1 Zn, 2 H, 2 Cl
__Zn(s) + __HCl  1 ZnCl2 + __H2(g)
1 Zn(s) + 2 HCl  1 ZnCl2 + __H2(g)
1 Zn(s) + 2 HCl  1 ZnCl2 + 1 H2(g)
Examples:
__Al + __O2  __Al2O2
__C2H6 + __O2  __CO2 + __H2O
__Fe2O3 + __H2SO4  __Fe2(SO4)3 + __H2O