Balancing and Writing Equations

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Chemical Reactions

• A basic definition of a chem rxn is:

The rearrangement of atomsIf it is there at the start, it is there at the end

• It is substance(s) changing into different substances

A chemical reaction

• The reactants (eggs, flour, etc.) have changed and are no longer eggs, flour, etc.

• There is a new substances called a product

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An Example• Eggs, flour, sugar, baking soda, and oil all in

various amounts combine together to form Cake!

http://images.google.com/imgres?imgurl=http://weblogs.variety.com/photos/new_york_wedding_cakes/cake2.jpg&imgrefurl=http://weblogs.variety.com/photos/new_york_wedding_cakes/cake2.html&usg=__wN3Fxd32xlwVDGfkpXYiSHJvuGQ=&h=405&w=300&sz=13&hl=en&start=18&tbnid=-0s3tNTPfi5nHM:&tbnh=124&tbnw=92&prev=/images%3Fq%3Dcake%26gbv%3D2%26hl%3Den%26safe%3Dactive

How do we write these?• We write these reactions with + signs and

signs.

Eggs + Flour + Baking Soda + Sugar

Cake

• Be Careful! The eggs, flour, etc. are not the same. They don’t exist anymore!!!!

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Here is an Example

Notice the motion

Evidence of Chemical Reactions

• Visual Clues A. Color changes B. Formation of a solid (precipitate) C. Flame occurs D. Bubbles are produced (gas)

• Temperature changes A. Heat is produced (exothermic) B. Heat is absorbed (endothermic)

Phases

• In most cases, phases must also be written. You should always include symbols for reactions you observe in the laboratory!

• Three common phases:

Solid ex: Cu(s)

Liquid ex: H2O(l)

Gas ex: Cl2(g)

Weird Phases

• These are solutions– Plasma (not common)

– Aqueous NaCl(aq)

Made of water and something dissolved in water

• What is the difference between Cu and Cu+2?

What does a solution look like?

To the naked eye it looks like a liquid, but upon closer inspection it is many substances mixed together

See an example

http://www.artuproar.com/uploads/9674/alien-eye.html

Another Example

Hydrogen gas combined with oxygen gas will produce dihydrogen monoxide liquid

H2 + O2 H2O

Let’s look back at the Help Pages

• Help Pages

http://www.rednoise.org/pdal/index.php?n=Main.Questions

BUT, matter is always conserved, atoms must be conserved!!!!!!!!

In order to make water, there needs to be 2 hydrogen molecules for every 1 oxygen molecule.

2 H2(g) + O2(g) 2 H2O(l)

To correctly write and balance an equation:

1. Formulas MUST be correct

2. There must be the same number of each kind of atom on each side of the arrow. This is done by using coefficients (numbers in front of a formula).

3. Do not change formulas to balance atoms!!

4. Follow a trial and error process. Balance each species one at a time. Be prepared to erase!!

BALANCING

Balancing simple equations

K + Cl2 KCl Fe + O2 Fe2O3

LiCl Li + Cl2 NaN3 Na + N2

NiO + Al Al2O3 + Ni C4H8 + O2 CO2 + H2O

Ag2O Ag + O2

B2O3 + Mg B + MgO

KBr + Cl2 KCl + Br2

Balancing Reactions containing polyatomic atoms

• ExampleLi3PO4 + MgCO3 Li2CO3 + Mg3(PO4)2

1. Keep the polyatomic ions together on both sides

2. Balance the metal ions first, or if they are balanced, the polyatomic ions first, metals last

If your formulas are correct, the equation should balanced

Balance:

Cu + AgNO3 Ag + Cu(NO3)2

NaI + Pb(NO3)2 NaNO3 + PbI2

Ca(CH3COO)2+ K2CO3 CaCO3+ KCH3COO

Water is decomposed by electricity to produce hydrogen and oxygen gases through a process called electrolysis.

When copper(II)chloride is dissolved in water and reacts with aluminum metal, copper metal and an aluminum chloride solution is produced.

Word Equations (writing equations from observations)

Lead(II)nitrate solution reacts with sodium sulfate solution to produce lead(II)sulfate solid and sodium nitrate solution.

Aluminum iodide solution reacts with lithium hydroxide solution to produce aluminum hydroxide solid and lithium iodide solution.

tetracarbon decahydride (butane) gas reacts with oxygen gas to produce carbon dioxide gas and water vapor.

Ammonia gas reacts with oxygen gas to produce nitrogen gas and liquid water.

Remember the following:

1. Diatomic elements (BrINClHOF)

[hydrogen gas, nitrogen gas, oxygen gas

AND all halogens in their elemental form]

2. The formulas and charges of the polyatomic ions

Sulfate Acetate

NitrateCarbonate

Hydroxide Ammonium

Questions?