In a physical change
- The identity and composition of the substance do not change
- The state can change or the material can be torn into smaller pieces
In a chemical reaction
- A chemical change produces one or more new substances
- There is a change in the composition of one or more substances
- Old bonds are broken and new bonds are formed
- Atoms in the reactants are rearranged to form one or more different substances
Changes that can be seen are evidence of
of a chemical reaction.
Chemists use a shorthand approach when writing the specifics of a chemical reaction
This approach is called the chemical equation
Reactants —–> Products
A chemical equation
Gives the chemical formulas of the reactants on the left of an arrow and the products on the right
Symbols used in chemical
equations show
- The states of the reactants
- The states of the products
- The reaction conditions
In a balanced chemical reaction
-Atoms are not gained or lost
-The number of reactant
atoms are equal to the number of product atoms
Chemical equations summary
- symbolic descriptions of chemical reactions.
- Two parts to an equation: reactants and products
A Chemical Equation must also be balanced
Coefficient
numbers in front of the chemical formulas; give ratio of reactants and products.
- CONVERSION FACTORS!!!
- Changing these changes the number of molecules
Formula subscript
- number in the middle of chemical formulas; give the number of each kind of atoms in individual molecules
- Changing these changes the identity of the compound
Chemical Equations must be balanced
There must be equal numbers of atoms of each element on both sides of the equation (both sides of the arrow)
Steps to balancing out a chemical equation
- Write the correct symbols and formulas for all of the reactants and products.
- Count the number of each type of atom on BOTH sides of the equation.
- Insert coefficients (numbers to the left of the compound formulas) until there are the equal numbers of each kind of atom on both sides of the equation.
Hints on Balancing Equations
- When there is no coefficient written, the coefficient is assumed to be 1
- To balance the equation insert COEFFICIENTS.
- NEVER alter the subscripts because that would change the chemical formula which would change the identity and properties of the substance.
- Start with atoms that only show up in only one compound on each side of the equation arrow.
- The only way to learn to balance equations is through practice
Chemical reactions can be classified as
- Combination reactions
- Decomposition reactions
- Single replacement reactions
-Double replacement
reactions
-Combustion reactions
In a combination reaction
- Two or more elements form one product
- Or simple compounds combine to form one product
In a decomposition reaction
One substance splits into two or more simpler substances
In a single replacement reaction
One element takes the place of a different element in a reacting compound
In a double replacement
Two elements in the reactants exchange places
In a combustion reaction
A compound such as carbon reacts with oxygen
