chemical reactions

CHEMICAL REACTIONS

Describing Chemical Change• Objectives

• Write equations describing chemical reactions using appropriate symbols

• Write balanced chemical equations when given the names or formulas of the reactants and products in a chemical reaction

Chemical Reactions-- Describing Chemical Change --

Chemical equation Expression representing a chemical reaction Reactants on the left side Products on the right side Arrow(s) connect(s) reactants and products

Examples

Chemical Quantities-- Describing Chemical Change --

Symbols (s): in solid state (l): in liquid state (g): in gaseous state (aq): an aqueous solution (substance dissolved

in H2O) or : heat is supplied to the

reaction : use of a catalyst (MnO2 in this

case) : yields or produces : reversible reaction

Catalyst Speeds up a reaction WITHOUT being used up

itself

Chemical Reactions -- Describing Chemical Change --

Skeleton equation Chemical equation that does not indicate the

relative amounts of reactants and products Does not necessarily follow the Law of

Conservation of Mass What does this law state?

Example: Frame + Wheel + Handle bar + Pedal

Bicycle

Write an example of your own. Raise your hand and have me come check it when you are finished.


Balanced equation Chemical equation in which mass is conserved Each side of the equation has the same number of atoms of each element.

Steps in writing a balanced equation Step 1: Write the skeleton equation Step 2: Count the number of atoms of each element on each side of the

equation Step 3: Add coefficients in front of each element in order to balance the

equation

Example Frame + 2 Wheels + Handle bar + 2 Pedals Bicycle

F + 2W + Hb + 2P FW2HbP2

NOTE: DO NOT CHANGE FORMULAS OF COMPOUNDS TO MAKE AN EQUATION BALANCED.


Example 1 “Iron (III) chloride reacts with sodium

hydroxide to produce iron (III) hydroxide and sodium chloride.” Step 1: Write the skeleton equation Step 2: Count the number of atoms of each

element on each side of the equation Step 3: Add coefficients in front of each

element in order to balance the equation


Example 2 Skeleton: FeCl3 + NaOH Fe(OH)3 + NaCl

Balanced:


Example 3 “Copper (II) sulfide reacts with oxygen gas to

produce copper and sulfur dioxide.” Write the skeleton equation for the above

reaction. Balance the above reaction. (Don’t forget to

count the atoms on each side of the equation)


Example 4

Skeleton: CuS + O2 Cu + SO2

Balanced:

Chem balancer Directions

Directions: 1. Start Internet Explorer and in the search bar

type “chem balancer” 2. Click on the first link “Classic Chembalancer” 2. Click ‘Directions’. Read and understand the

directions. 3. Click ‘OK’. 4. Click on ‘Start Game’ 5. Try entering some numbers in the text boxes

in front of each molecule. What happens?

chemical reactions

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