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Writing Chemical Equations. Text Reference: Ch 7, Section 2 - 3. Chemical Reactions. A chemical reaction is a process. What does this mean? Give some examples of processes Is baking a cake a process? Name some ingredients of baking a cake What is the product of this baking a cake process?

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chemical reactions
Chemical Reactions
  • A chemical reaction is a process.
  • What does this mean?
  • Give some examples of processes
  • Is baking a cake a process?
  • Name some ingredients of baking a cake
  • What is the product of this baking a cake process?
  • The cake – duh!
  • What symbol do we use to show processes?
chemical reactions1
Chemical Reactions
  • In a chemical reaction, the  can be read as “produces” or “yields”
  • With a chem. Rx. (chemical reaction) something(s) new is produced from other chemical ingredients.
  • The arrow indicates the process of burning, combining, exploding, disintegrating….
  • To the left of the arrow is what goes into the reaction:
  • Reactants, separated by + signs
  • On the right: ?
  • Products, also separated by + signs
chemical reactions2
Chemical Reactions
  • Convert baking a cake into a chemical reaction
  • Flour(s) + water(l) + eggs(s) + milk(l), etc  cake(s) + good aroma filling the kitchen!(g)
  • Ingredients are reactants
  • Cake + aroma = products
  •  = heat (produces, yields)
  • You know a chemical reaction has occurred because you can’t reverse it.
old prerequisites for writing chemical equations things you should must already know
Old Prerequisites for Writing Chemical Equations(things you should/must already know)
  • Elements from periodic table
  • How to write ionic and covalent compound names
  • How to interpret word problems
new prerequisites for writing chemical equations
New Prerequisites for writing chemical equations
  • (l) = liquid state
  • (s) = solid state
  • (g) = gas
  • (aq) = aqueous (dissolved in water; solution)
  • The BrINClHOF’s(for a family name)
  • Guess what elements these are
  • bromine,
  • iodine,
  • nitrogen,
  • chlorine,
  • hydrogen,
  • oxygen,
  • fluorine
new prerequisites for writing chemical equations1
New Prerequisites for writing chemical equations
  • The BrINClHOF’s(for a family name)
  • Always exist in pairs, when not combined with other elements
  • Gas at room temp.
  • Referred to by their normal chemical name even though they’re combined
  • ie. “chlorine” = Cl2(g)
  • “oxygen” = O2(g)
  • AKA: HONey and the Halogens (for a band name)
  • AKA: Hyd-7 (for a card game)
other things helpful to know
Other Things Helpful to Know
  • When metals are just named (i.e., “lead”) this is simply the solid pure element (i.e., Pb(s))
  • When things are “bubbled in” that means a gas form of that element is being added:
  • Ex: “hydrogen is bubbled into a solution of…”
  • Is written as: H2(g) + …  …
  • “Solutions” are aqueous. Ex: “ a solution of lead(II)chloride…” =
  • PbCl2(aq)
  • Acids are always “aqueous”
rules for writing chem equations
Rules for Writing Chem Equations
  • Figure out which are reactants and which are products.
  • Write chemical formulas for all substances, separated by the 
  • Add state of matter to each substance
  • Balance equation
writing chem equation examples
Writing Chem. Equation Examples
  • Zinc and aqueous lead(II)nitrate are combined in an aqueous solution to produce zinc nitrate and a lead precipitate.
  • zinc and lead(II)nitrate are reactants; zinc nitrate and lead are products
  • Zn + Pb(NO3)2 Zn(NO3)2 + Pb
  • Zn(s) + Pb(NO3)2(aq) Zn(NO3)2(aq) + Pb(s)
  • Balance: coming right up!
writing chem equation examples1
Writing Chem. Equation examples
  • Carbon tetrachloride may be prepared by the reaction of natural gas, methane, and chlorine in the presence of ultraviolet light. Hydrochloric acid (HCl) is also a product of this reaction.
  • Carbon tetrachloride and hydrochloric acid are the products; methane and chlorine are the reactants
  • CH4 + Cl2 CCl4 + HCl
  • CH4(g) + Cl2(g)  CCl4(s) + HCl(aq)
  • To Balance…(explained in the following slides)
  • CH4(g) + 4Cl2(g)  CCl4(s) + 4HCl(aq)
balancing chemical equations
Balancing Chemical Equations
  • Big Idea: Law of Conservation of Matter
  • Matter cannot be created or destroyed
  • Number of atoms of a certain element must be equal on reactant and product side.
  • A balanced chemical equation shows the ratio of elements from one side to other
rules for balancing chem eqns
Rules for Balancing Chem. Eqns.
  • Write unbalanced equation
  • Once unbalanced equation is written, NEVER CHANGE THE SUBSCRIPTS
  • Only add coefficients to front of compound
    • Coefficients multiply everything in the compound by that amount
  • Work with most complex molecule first, and save simplest for last
  • If you have an odd # of elements on one side, multiply entire eqn by 2, and continue
review reading molecular numbers
Review: reading molecular numbers
  • How many oxygen atoms in each of the following?
  • O2
  • 2
  • H2O
  • 1
  • PO43-
  • 4
  • 2H2SO4
  • 8
  • 2Ca(OH)2
  • 4
  • 3Ca3(PO4)2
  • 24
balancing examples
Balancing examples
  • O3  O2
  • You need the same number of O’s on both sides
  • 2O3  3O2
  • 6 = 6
  • Balance: H2 + O2  H2O
  • 2H2 + O2  2H2O
  • H’s : 4 O’s : 2
balancing a combustion example
balancing a Combustion example
  • Combustion of ethane
  • C2H6 + O2 CO2 + H2O
  • Which is most complex?
  • Ethane – so balance those elements first
  • C2H6 + O2 2CO2 + 3H2O
  • Now you have odd number of O’s
  • Multiply entire eq’n by 2
  • 2(C2H6 + O2 2CO2 + 3H2O)
  • 2C2H6 + 2O2 4CO2 + 6H2O
  • Balance O’s
  • 2C2H6 + 7O2 4CO2 + 6H2O
  • Make a T chart to double check balance of all elements on both sides
classifying chemical reactions
Classifying Chemical Reactions
  • You will need to be able to identify and balance the following types of chemical equations:

1) Synthesis

2) Decomposition

3) Single Replacement

4) Double Replacement

5) Combustion

classifying chemical reactions1
Classifying Chemical Reactions
  • Combustion - “burning” (but not necessarily with flames) to release energy from a compound
  • The energy is stored in the bonds of the compound being “burned”
  • Oxygen is almost always one of the reactants
  • Produces carbon dioxide and water
  • Ex: cellular respiration
  • Glucose + oxygen  water + carbon dioxide + ENERGY
classifying chemical reactions2
Classifying Chemical Reactions
  • Synthesis:
  • Putting things together
  • 2H2 + O2 2H2O
  • Can you think of another example from biology?
  • Decomposition
  • Breaking compounds down
  • 2H2O2H2 + O2
  • What other rx type is also decomposition?
  • combustion
classifying chemical reactions3
Classifying Chemical Reactions
  • Single replacement:
  • One element “steals” partner from another
  • General format: AB + C  A + BC
  • 3SrO(s) + 2Al(s)  Sr(s) + Al2O3(s)
  • Double replacement:
  • like “Wife Swap”
  • AB + CD  AD + CB
  • (note: the cation always goes first)
  • CaF2 + H2SO4 CaSO4 + 2HF
solubility ch 8 section 1
Solubility Ch 8 section 1
  • Soluble dissolves (in water)
  • Insoluble doesn’t dissolve (in water)
  • Precipitate solids that form when two ions react in water to form an Insoluble compound
  • Precipitation/ing forming a solid
writing net ionic equations
Writing Net Ionic Equations
  • Complete ionic equation shows all strong electrolytes (soluble, aqueous) as ions.
  • Spectator Ion an ion present in a solution that does not participate in a rx.
  • Net ionic equation includes only those components that participate in the rx
writing net ionic equations1
Writing Net Ionic Equations
  • Write the reactants with (aq) next to them
  • write the products,
  • balance equation
  • Determine if a reaction occurs by using solubility rules (for DR rxn) or activity series (for SR rxn). If no reaction occurs, write No Reaction
  • Write complete ionic eq’n., keeping precipitate together, but separating all other soluble ions.
  • Cancel out spectator ions from reactant & product sides
  • Rewrite eq’n, leaving out canceled ions.
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