Reactions and Empirical Formulas

Question 1

Empirical Formulas

Answer 1

-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

Question 2

Steps to Finding Empirical Formulas

Answer 2

poem:
percent to mass
mass to mole
divide by small
multiply til whole

Question 3

Steps to finding molecular formulas

Answer 3

1. find empiral formula
2. find molar mass of empircal formula
3. divide the molar mass molecular formula/molar mass of an empirical formula
4. multiply subscript with / answer

Question 4

What is a chemical reaction

Answer 4

a process in which 1 or more substances are changed into different substances, bonds are either put together, take apart or rearranged

Question 5

substance that goes into a reaction

Answer 5

reactants (on the left)

Question 6

substances that are made by a reaction

Answer 6

products (on the right)

Question 7

what is the arrow in equations

Answer 7

stands for yields (makes, produces, becomes, evolves)

Question 8

evidence of chemical reactions (light)

Answer 8

exothermic, you feel the heat in the surroundings

Question 9

absorption of energy

Answer 9

endothermic, surroundings feel colder than reactants

Question 10

more evidence of chemical reactions

Answer 10

• production of gas
• color change
• formation of a precipitate (an insoluble substance that falls to the bottom of the reaction)

Question 11

why balance equations

Answer 11

1st law of thermodynamics (mass can’t be created or destroyed)

Question 12

Rule 1 for Balancing Equations

Answer 12

coefficients are written in front of substances

Question 13

Rule 2 for Balancing Equations

Answer 13

only change coefficients!!

Question 14

Rule 3 for Balancing Equations

Answer 14

don’t touch the formulas or subscripts

Question 15

Rule 4 for Balancing Equations

Answer 15

if you cannot balance an equation it is not a real equation

Question 16

single replacement

Answer 16

one element replaces a less active element in a compound (AX+B –> BX+A)

Question 17

one rule for a single replacement

Answer 17

all hydrogens get kicked from acids, and only 1 hydrogen gets kicked from water

Question 18

what is a substances activity

Answer 18

its a measure of its reactivity with various substances (use activity series)

Question 19

double replacement

Answer 19

the ions of two compounds trade place in an aqueous solution. positive cation goes with negative anions
AB+CD–>AD+CB

Question 20

rules for a single replacement

Answer 20

-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

Question 21

what do you do if there is a diatomic molecule (single replacement)

Answer 21

put a subscript of 2 on them

Question 22

Decomposition

Answer 22

-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

Question 23

What is decomposing a substance using electricity called

Answer 23

its called electrolysis

Question 24

Synthesis

Answer 24

two or more substances combine to form a new compound (many reactants one product)
2Mg+O2–>2MgO

Question 25

Combustion Reaction

Answer 25

a substance combines with oxygen, releasing a large amount of energy (any burning reaction) 2H2+O2-->2H2O