Text Reference: Ch 7, Section 2 - 3

Writing Chemical Equations

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?

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

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.

Elements from periodic tableHow to write ionic and covalent

compound namesHow to interpret word problems

(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

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)

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 aqueous

1. Figure out which are reactants and which are products.

2. Write chemical formulas for all substances, separated by the

3. Add state of matter to each substance

4. Balance equation

Zinc and aqueous lead(II)nitrate are combined in an aqueous solution to produce zinc nitrate and a lead precipitate.

1.zinc and lead(II)nitrate are reactants; zinc nitrate and lead are products

2.Zn + Pb(NO3)2 Zn(NO3)2 + Pb3.Zn(s) + Pb(NO3)2(aq) Zn(NO3)2(aq) +

Pb(s)4.Balance: coming right up!

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.

1.Carbon tetrachloride and hydrochloric acid are the products; methane and chlorine are the reactants

2.CH4 + Cl2 CCl4 + HCl3.CH4(g) + Cl2(g) CCl4(s) + HCl(aq)4.To Balance

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

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

How many oxygen atoms? O2 2 H2O 1 PO4

3-

4 2H2SO4 8 2Ca(OH)2 4 3Ca3(PO4)2 24

O3 O2You 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

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 eqn 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

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 6) Acid-Base 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 waterEx: cellular respirationGlucose + oxygen water +

carbon dioxide + ENERGY

Synthesis: Putting things together2H2 + O2 2H2OCan you think of another example

from biology?

DecompositionBreaking compounds down2H2O2H2 + O2What other rx type is also

decomposition?combustion

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

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

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

1.1. Write the reactants with (aq) next to themWrite the reactants with (aq) next to them2.2. write the products, write the products, 3.3. balance equationbalance equation4.4. Determine if a reaction occurs by using Determine if a reaction occurs by using

solubility rules (for DR rx.) or activity series solubility rules (for DR rx.) or activity series (for SR rxs.). If no reaction occurs, write (for SR rxs.). If no reaction occurs, write No No ReactionReaction

5.5. Write complete ionic eqn., keeping Write complete ionic eqn., keeping precipitate together, but separating all other precipitate together, but separating all other soluble ionssoluble ions.

6.6. Cancel out spectator ions from reactant & Cancel out spectator ions from reactant & product sidesproduct sides

7.7. Rewrite eqn, leaving out canceled ions.Rewrite eqn, leaving out canceled ions.