Chemical Equations Writing and Balancing Equations Chemical Reactions

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Chemical Equations Writing and Balancing Equations

Chemical Equations Writing and Balancing Equations

Chemical Reactions A chemical reaction is the process by which one or more substances

Chemical Reactions A chemical reaction is the process by which one or more substances are changed into different substances.

Reactants are the beginning substances in a chemical reaction (left of arrow). Products are

Reactants are the beginning substances in a chemical reaction (left of arrow). Products are the substances produced in a chemical reaction (right of the arrow).

Chemical equations – represent chemical reactions using formulas and symbols for the substances, their

Chemical equations – represent chemical reactions using formulas and symbols for the substances, their states, and other conditions. (NH 4)2 Cr 2 O 7 (s) → N 2 (g) + Cr 2 O 3 (s) + 4 H 2 O (reactant) (products)

Law of Conservation of Mass – states that matter can neither be created or

Law of Conservation of Mass – states that matter can neither be created or destroyed in a chemical reaction. It can only change forms. Antoine-Laurent de Lavoisier

Therefore, the same number of each kind of atom must be found on the

Therefore, the same number of each kind of atom must be found on the left and on the right sides of a chemical equation. 2 H 2 + O 2 2 H 2 O This is accomplished by adding coefficients to the front of compounds and elements. Do not change subscripts.

Example: assuming all reactants are used completely 2 H 2 + O 2 →

Example: assuming all reactants are used completely 2 H 2 + O 2 → 2 H 2 O 5 grams 40 grams __ grams

Writing Balanced Equations Step 1 – Determine the reactants and products. Important – The

Writing Balanced Equations Step 1 – Determine the reactants and products. Important – The following elements exist as diatomic molecules in their free (uncombined) state: O 2, H 2, N 2, Cl 2, Br 2, F 2, and I 2

Step 2 – Write the chemical equation with the correct symbols for all reactants

Step 2 – Write the chemical equation with the correct symbols for all reactants and products. Step 3 – Balance the equation by adding coefficients to the front of formulas Hint: Balance elements that appear more than once on a side last.

Step 4 – Add symbols, when appropriate. COMMON SYMBOLS àyields (separates reactants from products)

Step 4 – Add symbols, when appropriate. COMMON SYMBOLS àyields (separates reactants from products) heat required (this symbol is placed over the arrow) (l) liquid (aq) aqueous (dissolved in water) (g) gas ( an is sometimes used for a gas product)

(s) solid (and is sometimes used for a precipitate) (cr) crystalline solid **Note: A

(s) solid (and is sometimes used for a precipitate) (cr) crystalline solid **Note: A formula over the yield arrow indicates a catalyst.

Example 1

Example 1

Example 2 CH 3 OH (l) + O 2 (g) → CO 2 (g)

Example 2 CH 3 OH (l) + O 2 (g) → CO 2 (g) + H 2 O (g) Example 3 Liquid water is formed from the combining of hydrogen and oxygen gases. (Write the Chemical Equation)