reaction types and chemical equations chemical reactions
TRANSCRIPT
Reaction Typesand
Chemical Equations
Chemical Reactions
Describing a Chemical Reaction
Indications of a Chemical Reaction
Evolution of heat, light, and/or sound
Production of a gas
Formation of a precipitate
Color change
Signs of Chemical Reactions
There are five main signs that indicate a chemical reaction has taken place:
change in color change in odor production of newgases or vapor
input or releaseof energy
rele
ase
inpu
t
formation of precipitate
Chemical Reactions
The starting substances turn into different substances by rearranging the atoms.
Mass is conserved in chemical reactions.
Starting substances = reactants Ending substances = products
5 Major Types of Chemical Reactions
Synthesis two or more substances combine to
form one substance A + B → AB
Decomposition one substance breaks down into 2 or
more substancesAB → A + B
Replacement/Displacement
Single Replacement one element switches places with an
element in a compoundA + BC → AC + B
Double Replacement two elements in two compounds
exchange placesAB + CD → AD + CB
Combustion of a Hydrocarbon
Combustion is the burning of a substance in the presence of oxygen.
This reaction is very specific. O2 should always be a reactant. CO2 and H2O should always be products.
CH4 + 2O2 → CO2 + 2H2O
Chemical Equations
A chemical reaction can be described by a chemical equation.
As mass is conserved in a chemical reaction, the amount of each element involved must be equal on both sides.
Example:
2 2 22 2H O H O
The Law of Conservation of Mass
Mass is neither created nor destroyed during a chemical reaction. Mass is conserved.
The law was first shown to be true by French scientist Antoine Lavosier (1743-1794) by making careful measurements with sensitive analytical balance.
Equation: Massreactants = Massproducts
Skeleton Equation
Uses chemical formulas, but is not balanced
Na(s) + H2O(l) → NaOH(aq) + H2(g)
Subscripts in parentheses are states of matter.
s = solid l = liquid g = gasaq = aqueous solution
Balancing Chemical Equations Add coefficients in front of the chemical
formulas. The coefficients act as multipliers.
Never change the subscripts when balancing and equation!
__ Na(s) + __ H2O(l) → __ NaOH(aq) + __H2(g)
Laws about the Composition of Pure Substances
Law of Definite Composition A given compound always contains the
same, fixed ratio of elements.
Law of Multiple Proportions Elements can combine in different
ratios to form different compounds. If two elements form more than one
compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers.
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Pure Substances
For example…
Two different compounds, each has a definite composition.
Carbon, C Oxygen, O Carbon monoxide, CO
Carbon, C Oxygen, O Oxygen, O Carbon dioxide, CO2
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Example Problem
If 39.098 g of potassium reacts completely with 35.453 g of chlorine, what mass of potassium chloride is formed?
Example Problem
Determine if compound I and II are the same compound.
Compound I total mass = 76.00 gmass of Fe = 53.46 g mass of O = 22.54 g
Compound II total mass = 56.00 gmass of Fe = 43.53 g mass of O = 12.47 g