Chemistry Helpers
Formulas and Equations
Formulas and Equations

 

Chemical Formulas
1.    Chemical Symbols: each element has been assigned a one, two, or three letter symbol for its identification. The first letter is ALWAYS CAPITALIZED, any additional letters are always lower case.
2.    Diatomic Molecules: When writing the symbols of uncombined elements, almost all are written without a subscript – they are monatomic. Some elements exist in nature as two identical atoms covalently bonded into DIATOMIC MOLECULES. They are:  Br2I2N2Cl2H2O2F2    Be sure that whenever you write the formulas for these you write them as diatoms.
3.    Chemical Formulas: compounds are composed of combinations of elements chemically combined in definite proportions by weight (mass). 
a) Formulas: use chemical symbols and numbers to show both   qualitative and quantitative information about a substance.
1) Qualitative:  information that cannot be counted or measured (what elements are present)
 
2) Quantitativeinformation that can be either counted or measured (how much is present)
 
b) Types of formulas: Two basic types of formulas provide different types of information about a compound. 
1) Empirical Formulathe simplest integer ration in which atoms combine to form a compound CH2 
*Formulas for ionic substances are empirical formulas.
2) Molecular Formulathe actual ratio of atoms in a molecule C4H8
 
4.    Atoms, Compounds, and Ions
       a) Atoms and compounds are electrically neutral which means that  there are equal numbers of positive and negative charges   
b) Ions are not neutral and may be either positively or negatively charged. An ion that contains more protons than electrons has an overall  positive charge and is called a(n)  cation. An ion that contains less protons than electrons has an overall  negative charge and is called a(n)  anion
 
c) Polyatomic Ions (PAI): a group of atoms covalently bonded together possessing a charge. Parentheses are used to enclose PAIwhen there is more than one of the ions in a unit of a compound. The subscript written after the parentheses tells how many of the ions are present in the compound. **The subscript refers to each of the elements in the ion.
Example:   (NH4)+               (PO3)-
 
d) Hydrates: when water from some ionic solutions evaporates, the solute forms a crystal lattice that binds water within the structure. Such a compound is called a hydrate. These crystals have a definite number of water molecules for each unit of the compound. These water molecules are loosely held to the compound.   Example:    Barium Chloride dihydrate   BaCl2 • 2H2O

*The anhydrous (not hydrated) compound can be obtained by heating the crystals to drive off the water. In a chemical reaction, the water in a hydrate does not react. However, it adds mass to the compound. 

 

 Energy:

·        2 types of reactions dealing with energy
1.                Endothermic:
(inside) (heat)
·        Chemical reactions that absorb energy or heat
·        It feels cold to the touch
·        You’ll see energy added on the left hand side of the equations
i.e. ice packs
 
2.                Exothermic
(outside) (heat)
·        Chemical reactions that release energy
·        They feel hot to the touch
·        You’ll see energy on the right hand side of the equations
i.e. heat packs
 
Types of reactions
1.                Synthesis:
·        A combination of 2 or more substances to form a compound
·        A + B = C
·        i.e. 2 Na (l) + Cl2 (g) = NaCl
2.                Decomposition:
·        Opposite of synthesis
·        AB = A + B
·        i.e. 2 H2O (l) = 2 H2 (g) + O2 (g)
 
3.                Single Replacement:
·        One element takes the place of another
·        A + BC = AB + C
·        i.e. Cl2(aq) + 2 KBr (aq) = 2KCl (aq) + Br2 (aq)
 
4.                Double Replacement:
·        Elements in compounds change partners
·        AB + CD = AC + BD
·        i.e.Pb(NO3)2(aq) + 2KI(aq)=PbI2(s)+2KNO3(aq)
 
5.                Combustion:
·        Oxygen reacting with a hydrocarbon (CH) to produce Water, Carbon Dioxide and Energy
·        CH4 + 2O2 = CO2 + 2H20 + Energy
·        Incomplete Combustion is when there is not enough oxygen to react with the hydrocarbon. This produces Water, Carbon Dioxide, Carbon Monoxide, Carbon and Energy
 
 
 Evidence of a chemical reaction: How do we know a rex has taken place?
·        release of a gas   (baking a cake)
·        color changes (leaves in the fall)
·        formation of a precipitate (solid substance formed from solutions)·        changes in heat and light (candle burning)

 

 Writing Chemical Formulas

a)    Criss-Cross Method: For each element present, write the oxidation state (found in the top right corner of the periodic table). Next, criss-cross those numbers ignoring the sign. 
Example: sodium + chlorine
 Na+1 +  Cl-1      =     NaCl
 
1)    sodium + oxygen
 Na+1   +     O-2     =   Na2O
 
2)    calcium + chlorine
                            Ca+2    +   Cl-1     =     CaCl2
 
 
b)    Polyatomic Ions (Table E): Two or more atoms that are chemically combined and possess a net electric charge.  
 
Naming Chemical Formulas
a)    Binary Compoundscomposed of two elements
                                                                               I.      Metal + Nonmetalthe metallic element is named and written first (it keeps its name), the nonmetallic element is second and its ending is changed to –ide
                                                                            II.      Nonmetal + Nonmetalthe less electronegative element is named and written first (it keeps its name), the other element is second and its ending is changed to –ide. Prefixes are used to indicate the number of atoms of each nonmetal.
a.     Prefixes for nonmetals   1 mono-   
                                            2 di-  
                                            3 tri-
                                            4 tetra- 
                                                                         III.      Binary AcidsConsist of hydrogen plus some nonmetal
Prefix hydro- + stem name of the nonmetal + suffix –ic
Example: HCl hydrochloric acid
Example: HBr hydrobromic acid
 
b)   Ternary Compoundsconsist of three elements
                                                                               I.      Ternary Bases: Metallic ions combined with the hydroxide ion (OH)
     The name of the metallic base followed by the word hydroxide
Example: NaOH is sodium hydroxide
Example: Mg(OH)2 is magnesium hydroxide
 
 
                                                                             II.      Ternary Acids: hydrogen ions combined with polyatomic ions
     The name of the acid is from the polyatomic ion. 
·        If the polyatomic ion ends in –ite, the name of the acid ends In –ous.
Example: H2SO4 sulfuric acid
Example: HNO3   nitric acid
 
·        If the polyatomic ion ends in –ate, the name of the acid ends in –ic.
Example H2SO3   sulfurous acid
Example: HNO2 nitrous acid
           
c)    Stock System: In naming compounds of metals that have more than one oxidation number, the name of the metal is followed by a Roman numeral that represents the oxidation number in that compound.
Example: chromium III bromide CrBr3

Example: nitrogen IV oxide   NO2

 

Energy:
·        2 types of reactions dealing with energy
1.                Endothermic:
(inside) (heat)
·        Chemical reactions that absorb energy or heat
·        It feels cold to the touch
·        You’ll see energy added on the left hand side of the equations
i.e. ice packs
 
2.                Exothermic
(outside) (heat)
·        Chemical reactions that release energy
·        They feel hot to the touch
·        You’ll see energy on the right hand side of the equations
i.e. heat packs
 
Types of reactions
1.                Synthesis:
·        A combination of 2 or more substances to form a compound
·        A + B = C                                     *= represents 'yields'
·        i.e. 2 Na (l) + Cl2 (g) = NaCl
2.                Decomposition:
·        Opposite of synthesis
·        AB = A + B
·        i.e. 2 H2O (l) = 2 H2 (g) + O2 (g)
 
3.                Single Replacement:
·        One element takes the place of another
·        A + BC = AB + C
·        i.e. Cl2(aq) + 2 KBr (aq) = 2KCl (aq) + Br2 (aq)
 
4.                Double Replacement:
·        Elements in compounds change partners
·        AB + CD = AC + BD
·        i.e.Pb(NO3)2(aq) + 2KI(aq)=PbI2(s)+2KNO3(aq)
 
5.                Combustion:
·        Oxygen reacting with a hydrocarbon (CH) to produce Water, Carbon Dioxide and Energy
·        CH4 + 2O2 = CO2 + 2H20 + Energy
·        Incomplete Combustion is when there is not enough oxygen to react with the hydrocarbon. This produces Water, Carbon Dioxide, Carbon Monoxide, Carbon and Energy
 
 
 
Evidence of a chemical reaction: How do we know a rex has taken place?
·        release of a gas   (baking a cake)
·        color changes (leaves in the fall)
·        formation of a precipitate (solid substance formed from solutions)
·        changes in heat and light (candle burning)

 

Balancing Chemical Equations notes:
Rules:
1.      Check equations by counting atoms on each side of the equation
2.      Start by putting 1 in front of the most complex compound
3.      Balance elements in multiple reactants or products last
4.      Use whole number coefficients (otherwise multiply)
5       Don’t touch the subscripts!!!
 
 
Law of conservation of mass:
· matter / energy is neither created nor destroyed
 
 
Polyatomics:
· if the same polyatomic appears on both sides of the equation, treat the polyatomic as if it were an atom (a whole unit - don't break it up)
 
example:
1.                  2Li (s) + Br2 (l) = 2 LiBr (s)  type of reaction: synthesis


Write Your Questions Below



NO2 +CO----NO + CO2 describes nitrogen and carbon monoxide gases reacting to form nitrogen monoxide and carbon dioxide. NO3 is an intermediate produce. Propose a mechanism for the reaction?
May 5, 2014

One possible solution is that the Nitrogen Dioxide would react with another:  NO2 + NO2

This would result in the formation of Nitrogen Trioxide and Nitrogen Monoxide: NO3 + NO

The Nitrogen Trioxide would then react with the Carbon Monoxide:  NO3 + CO

This would result in the formation of Nitrogen Monoxide and Carbon Dioxide: NO + CO2

May 15, 2014 -  Replied By Expert

500ml of 2.00ml NaOH solution has a density of 1.90g/ml. What is the concentration of this solution in: a)percentage by mass b)Molality
April 14, 2014
  •  Are you referring to a 2M solution of NaOH?Or perhaps 2.00g of NaOH? Since the unit seems to be incorrect, here are a few ways to solve your question:
  • Determine the gram formula mass for NaOH and then determine how many moles you have using the formula moles = given mass/gram formula mass
  • Using the density formula D=m/v you can rearrange it to determine the mass of the solvent in kg: D(v) = m and then convert to kg.
  • Finally you can find the molality using the formula molality = moles of solute/mass of solvent
  • To find the percent composition you need to use the formula % comp = (mass part/mass whole) x 100
April 15, 2014 -  Replied By Expert

how do you calculate the percent of gasoline in gasohol if 93.4 gal of gasohol contains 7.62 gal of ethyl alcohol
January 29, 2014

Hi, to calculate the percent composition of something you will use the following formula:

percent composition = (mass part)        x 100

                                       (mass whole)

 

With your numbers you would calculate the percent of ethyl alcohol, however your question refers to the percent of gasoline so you must subtract the answer from 100 to find out the percent of gasoline.

January 31, 2014 -  Replied By Expert

 
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