Balancing Chemical Equations

​Balancing Chemical Equations

​Evidence for a Chemical Reaction

• ​color changes

• a solid forms (precipitate)

• bubbles form

• heat or a flame is produced

• heat is absorbed (becomes cold)

​Chemical Equation

​Chemical Reaction -- the rearrangement of the ways in which atoms are grouped.

Chemical Equation -- A representation of a chemical reaction showing the relative numbers of reactant and product molecules.

​Reactants -- chemicals present before the reaction and are shown to the left of the arrow.

Products -- chemicals present after the reaction and are shown to the right of the arrow.

Multiple Choice

Which of the following chemical formulas are the reactants?

• $$CH_4$$

• $$CH_4\ \ and\ \ 2O_2$$

• $$CO_2$$

• $$CO_2\ \ and\ 2H_2O$$

Multiple Choice

Which of the following chemical formulas are the products?

• $$2O_2$$

• $$CH_4\ and\ 2O_2$$

• $$CO_2$$

• $$CO_2\ and\ 2H_2O$$

​Conservation or Matter

​In a chemical reaction, atoms are neither created nor destroyed.

All atoms present in the reactants must be accounted for among products

​Subscripts

A subscript is a small number written at the bottom of the symbol. If the number is on the right side, it depicts the number of atoms of the element present in the molecule.

​Counting Atoms

​Subscripts tells us how many atoms of a certain element are in a chemical equaiton.

• ​Coefficients are used to balance chemical equations.

• The smallest integers (whole numbers) are used to balance the equations.

• The coefficient must go in front of the chemical formula.

• The number 1 is never used as a coefficient.

​Coefficients

​Coefficients are used to balance chemical equations. The coefficient multiplies everything in the chemical formula.

In the equation above, there are 4 hydrogen and 2 oxygen to the left of the arrow and 4 hydrogen and 2 oxygen to the right of the arrow.

​ 4 = H = 4

2 = O = 2

Multiple Choice

_______________ are numbers used to balance chemical equations.

• subscripts

• coefficients

• reactants

• products

Multiple Choice

How many hydrogen atoms are in the formula for glucose, C₆H₁₂O₆ ?

• 6

• 12

• 18

• 24

Multiple Choice

How many atoms of oxygen are in the chemical formula for sulfuric acid, H₂SO₄ ?

• 1

• 2

• 3

• 4

Multiple Choice

How many atoms of oxygen are in the chemical formula for potassium carbonate?

2K₂CO₃

• 2

• 3

• 4

• 6

Multiple Choice

How many atoms of hydrogen are on the reactant side of the balanced chemical listed below?

2H₂O → 2H₂ + O₂

• 1

• 2

• 3

• 4

Multiple Choice

How many atoms of oxygen are in the product side of the balanced chemical equation below?

H₂SO₄ + 2NaOH → 2H₂O + Na₂SO₄

• 2

• 4

• 6

• 8

​How to Balance a Chemical Equation.

Multiple Choice

What coefficients are needed to balance the following chemical equation?

__H₂O → __H₂ + __O₂

• 1, 1, 1

• 2, 2, 2

• 2, 2, 1

• 2, 2, 3

Multiple Choice

What coefficients are needed to balance the following chemical equation?

__Zn + __HCl → __ZnCl₂ + __H₂

• 1,1,1,1

• 1,2,1,1

• 2,1,2,2

• 2,1,2,1

Multiple Choice

What coefficients are needed to balance the following chemical equation?

__Fe + __ AgNO₃ → __ Ag + __ Fe(NO₃)₃

• 1,1,1,1

• 1,2,1,2

• 1,3,3,1

• 3,1,3,1