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4.01a Balance the following equation 1

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化学

肯塔基大学

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This course is designed to cover subjects in advanced high school chemistry courses, correlating to the standard topics as established by the American Chemical Society. This course is a precursor to the Advanced Chemistry Coursera course. Areas that are covered include atomic structure, periodic trends, compounds, reactions and stoichiometry, bonding, and thermochemistry.

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Jun 21, 2017

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从本节课中

Week 4

We will explore how compounds react with one another to form new substances and then write balanced chemical equations to represent what is happening in a reaction. We will explore several different types of reactions including precipitation, acid-base, oxidation-reduction, and combustion reaction.

4.01 Writing Balanced Chemical Equations 12:10

4.01a Balance the following equation 1 2:57

4.01b Balance the following equation 2 3:32

4.02 Aqueous solutions 12:52

4.03 Solubility of ionic compounds 6:23

4.04 Precipitation Reactions6:34

4.05 Molecular, Ionic and Net ionic Equations 6:14

4.05a Net ionic equation 5:46

4.06 Acid-base reactions 15:16

4.07 Oxidation-reduction reactions 16:49

4.07a Oxidation Numbers 2:25

4.07b Oxidized and Reduced species identification 2:37

4.08 Combustion Reactions 5:35

4.08a Balance the following equation 3 4:12

教学方

Dr. Allison Soult
Lecturer
Dr. Kim Woodrum
Sr. Lecturer

Balance the following equation.

Whenever I balance an equation,

I always make a list of all the elements present in the reaction so

that I can tally how many I have of each element on either side of the equation.

One thing I notice in this equation.

I see phosphate on the left and phosphate on the right, and

I don't see any other phosphorus or oxygen anywhere in the equation.

Likewise, with CN, I see it on the left and the right.

Both have CN, and

I see neither carbon nor oxy, nitrogen present anywhere else in the reaction.

So when I write my list of elements I'm actually going to leave the phosphate and

the cyanide written as those polyatomic ions.

Now if you expand it and write it as phosphorus, oxygen, carbon and

nitrogen, you will still get the exact same result.

Sometimes we can't do this.

If for example I have phosphate on the left side, but

on the right I had phosphorous and water and some other reactants or

products, then I wouldn't be able to keep them written as the polyatomic ions.

So this is just a little bit of a shortcut when you notice this is happening.

So here I have hydrogen, phosphate, sodium, and CN.

So on the left side I have three hydrogens,

one phosphate, one sodium, and one cyanide.

On the right side of the equation I have one hydrogen,

one phosphate, three sodium, and one cyanide.

So I see that I have a couple of things that are out of balance.

So I'm going to start with the hydrogen for

no other reason than because it's listed first.

And I'm going to add a coefficient in front of the HCN so

that now I have three hydrogens on the right, but

that also changed the number of CNs on the right to three.

So now my hydrogens and my phosphates are balanced, but

the sodium and the cyanide are not.

So now I need to add a 3 in front of NaCN.

So that gives me three sodiums and three cyanides.

And now it appears that my equation is balanced.

And so I can go back and review this just to make sure, and

we see we have three hydrogens on the left, three hydrogens on the right.

And I'll actually go through this elementally so

that way you can see that it does work to leave these as polyatomic ions

when the polyatomic ions remain intact from the left to the right.

So here I have phosphorus, one phosphorus on the left, one phosphorus on the right.

Four oxygens on the left, four oxygens on the right.

Three sodiums on the left, three sodiums on the right, three carbons, and

three carbons.

Three nitrogens on the left and three nitrogens on the right.

So I see that I have a balanced chemical equation, and always remember to go back

and check at the end just to make sure you haven't lost something along the way.

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