Chemistry question!?

Question

can someone please explain to me redox? more importantly though can anyone explain to me how to do stoichiometry??

Answer 1

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Fun with Stoichiometry!
I know what you’re thinking: You hate stoichiometry. You can’t pronounce it, you
can’t spell it, and it involves all kinds of calculations that drive you crazy. Your
friends all hate it, too, and your teacher keeps using the word “stoichiometry” like
it’s some kind of magic word.
OK… take a deep breath. We’re about to start over from scratch, so forget
everything you know about stoichiometry (that is, if you knew anything to start
with), because we’re going to start over.
What is stoichiometry, anyway?
The best definition for stoichiometry is this: It’s a way of figuring out how much
stuff you’re going to make in a chemical reaction, or how much stuff you’ll need
to make a chemical reaction do what you want.
This isn’t scary at all. Let’s think of my favorite chemical reaction: Making
peanut butter and jelly sandwiches (OK… maybe it’s not a chemical reaction, but
the idea is the same). When I’m really hungry, I do stoichiometry during this
process. For example, if I have ten pieces of bread in my house, stoichiometry
converts the amount of break I have (ten pieces) into the number of sandwiches I
can make (five). This is exactly the same thing that you do in chemistry, except
that the conversion factors are a little bit more challenging.
How do I get started?
Before I can even answer this question, you’ll need to understand how I do
calculations. Since stoichiometry calculations are exactly the same thing as unit
conversions, you should review how to do T-chart unit conversions at
http://misterguch.brinkster.net/unitconversions.html before continuing. I’ll wait
patiently here while you do that.
OK… I know you didn’t visit that link. Seriously, go visit that link, or my
explanation won’t make any sense. You’ll be just as frustrated as you were
before, and you don’t want that, do you? Of course not! Go visit that link, learn
how to do unit conversions using my fancy method, and then come on back.
Now that you understand how to do unit conversions using my handy dandy
method, I’m going to throw a big scary diagram at you. Please don’t freak out –
it’s a lot easier to use than it looks:
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Believe it or not, this is the ONLY thing you have to memorize to do stoichiometry
calculations (assuming you actually followed the link I gave you earlier – if you
didn’t do it then, do it now or you won’t understand what I’m talking about later).
Before we do anything, let’s go through what all the chemical terms on this
diagram mean.
reactant: The thing that you start with in the reaction. For making PB&J
sandwiches, bread is a reactant. For the equation 2 H2 + O2 à 2 H2O, both H2
and O2 are reactants.
product: The thing you make in the reaction. For making PB&J sandwiches, the
sandwich is your product. For the equation 2 H2 + O2 à 2 H2O, water is your
product.
mole ratio: The ratio of the product and reactant in a chemical reaction. The
numbers that fit into this ratio are pulled directly out of the balanced equation for
the reaction. I realize that this doesn’t make any sense to you yet, so don’t worry
too much about this right now.
PV=nRT (and all the stuff written around it): If you’ve studied the gas laws,
you already know how to convert liters to moles (using pressure and temperature
and whatnot). If you need a review of how to do this, visit my handy tutorial page
at http://misterguch.brinkster.net/gaslaws.html – if you’ve never seen it before,
then the only thing you need to know about this are the words “22.4 L in 1 mole.”
molar mass: The molar mass is also known as the “molecular mass”,
“molecular weight”, and “gram formula mass.” If you don’t remember what this
means, check out my tutorial page on the subject at
http://misterguch.brinkster.net/molarmass.html.
That’s great, Mr. Guch – but now what do I do?
Hey, I’m getting to that! The diagram I gave you is nothing more than a map that
explains how to get from what you’ve been given in the problem to what you’ve
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been asked to figure out. (To see how this works using a simpler diagram, take a
look at http://misterguch.brinkster.net/molecalculations.html).
The idea is simple. Given the problem you’re trying to solve, figure out what box
in the diagram is your starting point and which diagram in your box is the ending
point. Then, using the T-chart method that we use for such things (once again, a
more complete description of this is at
http://misterguch.brinkster.net/unitconversions.html), we convert stepwise from
our starting box through each intermediate step until we reach our destination
box.
The best way to understand how this works is to just do an example.
Example: How many grams of water can I make from 25 grams of
hydrogen gas and an excess of oxygen gas, using the reaction 2 H2 + O2 à
2 H2O?
Answer: Let’s take this one step at a time!
Step 1: Figure out our starting and destination boxes.
Since we were given 25 grams of hydrogen in the problem, and hydrogen is a
reactant in this reaction, we will start at “grams of reactant” as our starting box.
Since we’re trying to figure out how many grams of water we can make and
water is a product, “grams of product” is our destination box:
One thing that students always find challenging is the term “excess of
[whatever].” When you see that in a problem, all this means is that there’s so
much of that reactant around that you don’t need to worry about it. Focus on the
other reactant. When we get to limiting reactant problems, then we’ll worry about
it!
Step 2: Move one box toward the destination box, doing the necessary
calculation.
In this case, we’re going to move from the “grams of reactant” box to the “moles
of reactant box.” Since we already know how to do this (from converting from
grams to moles using the T-chart method, as mentioned above and as described
For chemistry help, visit www.chemfiesta.com © 2006 Cavalcade Publishing, All Rights Reserved
in gory detail at http://misterguch.brinkster.net/molecalculations.html), we can
see that this is done like this:
Step 3: The dreaded mole ratio!
What’s a mole ratio? Don’t worry about that yet. What we’ll do is simply set up
our calculation from “moles of reactant” to “moles of product” just like we do with
every T-chart calculation and not even worry about the numbers we need for our
conversion factors. When we do that, we end up with:
Of course, we need to know what numbers to put in front of “moles water” and
“moles hydrogen.” These numbers are the numbers from in front of each formula
in the balanced chemical equation for this reaction. In our case, the reaction is
2 H2 + O2 à 2 H2O, so the number in front of “moles water” is “2” and the number
in front of “moles hydrogen” is also “2”. Putting these numbers into the equation,
we end up with:
Step 4: Move to the destination box.
If you understood all of this so far, then you probably understand what I mean
here. Do the calculation from “moles product” to “grams product”, which should
look like this:
Step 5: Do the math
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To do the math, simply multiply all the numbers on the top of the T together and
divide it by the multiplied numbers from the bottom. When you do this, you end
up with 225 grams of water. That’s your answer!
Limiting reagent problems:
Now that you know how to do regular problems of this sort, it’s time to figure out
how to do limiting reagent problems. These problems are of this general variety:
Problem: How many grams of water can I make from 22 grams of hydrogen
and 195 grams of oxygen?
Answer: Do two stoichiometry calculations!
The idea here is simple. Do two stoichiometry calculations. One will convert 22
grams of hydrogen to grams of water and the other will convert 195 grams of
oxygen to water. The answer which gives the smallest amount of product will be
the correct answer, and the reactant which gives you this answer is the “limiting
reagent” (because it ran out before the other one did).
Conceptually, we can see how this works with sandwiches. If I make a very
boring sandwich from 2 slices of bread and 1 slice of cheese, I can ask myself a
limiting reagent problem like this:
How many cheese sandwiches can I make using 500 slices of bread and 2
slices of cheese?
Now, this is a pretty simple question that you can solve in your head, but the idea
is the same. If you examine how you solve problems like this, you find that your
mental process figures out how many sandwiches you can make from 500 slices
of bread (250 sandwiches) and how many you can make from 2 slices of cheese
(2 sandwiches). Because you run out of cheese after 2 sandwiches, you can
only make 2 sandwiches no matter how much bread you have. In this question,
cheese was our “limiting reactant.”
Using your stoichiometry knowledge, do the calculation to see how much water
we can make from 22 grams of hydrogen and 195 grams of oxygen. I’ll wait
here.
OK… when you do this calculation, you end up with two different answers. Let’s
see those two calculations (I won’t go through each step because you already
know how to do this kind of problem):
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Since 110 grams of water is smaller than 198 grams of water, our answer is 110
grams of water. Because oxygen was the reactant that caused us to get this
answer, it is the limiting reagent.
I hope this helped you! I’ve got many handy stoichiometry worksheets for your
practicing pleasure on this page:
http://misterguch.brinkster.net/pra_equationworksheets.html.
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[e-mail]).

Answer 2

well as regerded to redox reaction : the reaction which is reduce and oxidised simultaneously is known as redox reactions.

and for stociometery it is not a one step method to tell you here
download this software here.
http://www.acdlabs.com/download/chemsk.html

if you want to thank me then visit my site and participate:
http://www.sihara.tk

Answer 3

Very interesting.

Answer 4

i think that that explains it all