CHEMICAL REACTIONS

Chapter 23

CHEMICAL REACTIONS Chemical reactions are happening all

around you A chemical reaction is a change in

which one or more substance become new substances

In all chemical reactions, the mass of the starting reactants equals the total mass of all productsWhat is this law called?

The Law of Conservation of Mass

WRITING EQUATIONS A chemical equation is

a way to describe a chemical reaction using chemical formulas and other symbols

On the left side of the equation are the reactants

On the right side of the equation are the products

Other symbols are also included to provide more information about the reactants, products, and reaction conditions

Symbol Meaning

Produces or yields

+ Plus

(s) Solid

(l) Liquid

(g) Gas

(aq) Aqueous

COEFFICIENTS Remember:

Matter can not be created or destroyed in reactions

There will be the same number of each type of atom on both sides of the equation

This is done by using coefficientsThese are the numbers found in front of

each compound

BALANCING EQUATIONS An equation will need to be balanced to

ensure that the same number of atoms of each element are on both sides of the equation

This is done by assigning coefficients

STEPS FOR BALANCING EQUATIONS Step 1: Write the equation Step 2: Count the atoms of each

element in both the reactants and the products

Step 3: Choose the coefficients necessary to balance the equation

Step 4: Recheck your answer

TYPES OF REACTIONS Combustion Reactions

A substance reacts with oxygen to produce energy in the form of heat and light

Synthesis ReactionsTwo or more substances combine to from

another substance Decomposition Reactions

A substance breaks down into two or more substance

TYPES OF REACTIONS Single Displacement

One compound replaces another in a compound

Double DisplacementTwo ionic compounds separate into ions and

then reform to form two new ionic compounds

The ions flip-flop Oxidation-Reduction Reaction

Reaction where one reactant loses electron(s) and the other gains electron(s)

The one losing electrons is oxidizedThe one gaining electrons is reduced

ENERGY AND CHEMICAL REACTIONS

Endergonic Reactions Exergonic Reactions

In some reactions, energy is needed to make the reaction happen

Energy will be absorbed as heat or light

They are endothermic

The reaction will feel cool to the touch

In other reactions, energy will be released when the reaction occurs

Energy will be released as heat or light

They are exothermic

The reaction will feel warm to the touch

ENERGY AND CHEMICAL REACTIONS