Reactions and Empirical Formulas Flashcards
Empirical Formulas
-the lowest whole # ratio of the elements in a compounds
-give proportions of elements but not the actual number of atoms
-used in mass spectrometry to identify compounds
Steps to Finding Empirical Formulas
poem:
percent to mass
mass to mole
divide by small
multiply til whole
Steps to finding molecular formulas
- find empiral formula
- find molar mass of empircal formula
- divide the molar mass molecular formula/molar mass of an empirical formula
- multiply subscript with / answer
What is a chemical reaction
a process in which 1 or more substances are changed into different substances, bonds are either put together, take apart or rearranged
substance that goes into a reaction
reactants (on the left)
substances that are made by a reaction
products (on the right)
what is the arrow in equations
stands for yields (makes, produces, becomes, evolves)
evidence of chemical reactions (light)
exothermic, you feel the heat in the surroundings
absorption of energy
endothermic, surroundings feel colder than reactants
more evidence of chemical reactions
- production of gas
- color change
- formation of a precipitate (an insoluble substance that falls to the bottom of the reaction)
why balance equations
1st law of thermodynamics (mass can’t be created or destroyed)
Rule 1 for Balancing Equations
coefficients are written in front of substances
Rule 2 for Balancing Equations
only change coefficients!!
Rule 3 for Balancing Equations
don’t touch the formulas or subscripts
Rule 4 for Balancing Equations
if you cannot balance an equation it is not a real equation
single replacement
one element replaces a less active element in a compound (AX+B –> BX+A)
one rule for a single replacement
all hydrogens get kicked from acids, and only 1 hydrogen gets kicked from water
what is a substances activity
its a measure of its reactivity with various substances (use activity series)
double replacement
the ions of two compounds trade place in an aqueous solution. positive cation goes with negative anions
AB+CD–>AD+CB
rules for a single replacement
-an ion can only replace another ion if its more active
-cation replaces cation, anion replaces anion
-anything above hydrogen will react with an acid
what do you do if there is a diatomic molecule (single replacement)
put a subscript of 2 on them
Decomposition
-on substance breaks down to produce two or more substances
-usually starts with the application of heat or other form of energy
2HGO–>2Hg+O2
What is decomposing a substance using electricity called
its called electrolysis
Synthesis
two or more substances combine to form a new compound (many reactants one product)
2Mg+O2–>2MgO
Combustion Reaction
a substance combines with oxygen, releasing a large amount of energy (any burning reaction)
2H2+O2–>2H2O
