Chemical Equations

1
Chemical Equations

• Unit Notes
• Foundations of Chemistry

2
A Quick Review

• Kinetic Molecular Theory
• Explains forces between molecules
• KMT can help predict the states of matter for a
  chemical
• States of Matter
• Are written to show the state of each chemical in
  a reaction
• Abbreviations are used after each species to show
  states
• Solid (s), Liquid (l), Gas (g), Aqueous (aq)
• Aqueous means dissolved in water

3
Chemical Equations

• Show a chemical reaction in abbreviated form
• Has multiple parts
• Reactants are the chemicals that are present
  before the reaction and are located on the left
  side of the reaction
• Products are the chemicals that are present after
  the reaction and are located on the right side of
  the reaction
• Yield sign is an arrow between the reactants and
  products that show the direction of the reaction

4
Schematic of a Reaction
Reactants ? Products
(Starting material)
(Ending material)
yields
C3H8 O2 ? CO2 H2O Propane and oxygen yield
carbon dioxide and water
5
Adding the States

• The states of each component are added to be more
  specific
• The chemical equation is then ready to be
  balanced.

C3H8(l) O2(g) ? CO2(g) H2O(g) Liquid propane
and oxygen gas yield carbon dioxide gas and water
vapor
6
Take a Sniff Demo

• Water and Salicylic acid in a test tube
• Add methanol and 2 drops of concentrated sulfuric
  acid
• Heat the test tube in a hot water bath
• Sniff the product!

7
Take a Sniff Reaction

• This type of reaction is called esterification
• An organic acid (salicylic acid) reacts with an
  alcohol (methanol) to produce an ester (methyl
  salicylate)
• What does it smell like?
• Methyl salicylate is also known as oil of
  wintergreen

8
A Kind Reminder ?

• An element that is alone is generally found as a
  single atom, BUT there are 7 elements that occur
  in pairs!
• HONClBrIF Happy NO-el or the Big 7
• H2, O2, N2, Cl2, Br2, I2, F2
• See the periodic table to see the 7
• These elements ALWAYS exist in pairs when
  isolated in nature!

9
Balancing Equations

• In order to follow the Law of Conservation of
  Mass, we need to make sure that the same number
  of atoms of each element are on each side of the
  equation.
• This is to show that matter was not created or
  destroyed in the reaction.

10
Balancing Equations (contd)

• In order to do this, we need to add coefficients
  (big numbers in front of the compound to show the
  number of molecules of that compound).
• Balance the following reaction
• ___H2(g) ___O2(g) ? ___H2O(g)
• Notice that there are 2 H and 2 O on the left,
  and 2 H and 1 O on the right.
• If we put a coefficient of 2 in front of H2O
  (to balance the O atoms), the H atoms will still
  not be balanced.
• If we place a 2 in front of H2 on the left
  side, the equation is balanced.

11
Balancing Equations (contd)

• Here is what we ended up with
• 2 H2(g) O2(g) ? 2 H2O(g)
• Notice that there are 4 H on both sides and 2 O
  on both sides!
• The equation is now balanced and follows the Law
  of Conservation of Mass!

12
Types of Chemical Reactions

• Chemical reactions can be classified into five
  different categories
• Synthesis reactions
• Decomposition reactions
• Single Replacement reactions
• Double Replacement reactions
• Combustion reactions

13
Synthesis Reactions

• Synthesis means to create
• Two or more reactants combine to form one product
• A X ? AX
• Example 2 Na Cl2 ? 2 NaCl
• Guy and girl meet and get married.

14
Decomposition Reactions

• Decomposition means to break down
• One reactant breaks down to create simpler
  molecules
• AX ? A X
• Example CaCO3 ? CaO CO2
• A married couple get divorced.

15
Single Replacement Reactions

• Single replacement refers to an element (by
  itself) trading places with another element in a
  compound.
• An element reacts with a compound to produce a
  new compound and a different element.
• A BX ? AX B
• Example 2 Na 2 HCl ? 2 NaCl H2
• A lover comes between a married couple and steals
  one away, leaving the other alone.

16
Double Replacement Reactions

• Double replacement refers to compounds trading
  partners.
• The cations trade anions to create two new
  compounds.
• AX BY ? AY BX
• A B are cations
• X Y are anions
• Example Ba(NO3)2 H2SO4 ? BaSO4 2 HNO3
• Two couples trade partners and run away with
  their new partners.

17
Combustion

• Combustion means to burn ?
• A fuel (usually a hydrocarbon) reacts with oxygen
  gas to form carbon dioxide and water vapor.
• CxHy O2 ? CO2 H2O
• Example CH4 2 O2 ? CO2 2 H2O
• Burn, baby, burn!