Stoichiometry with Molarity and STP

The past is coming back to haunt us!

MOLARITY AND STP!

this is insane

Let us review what we know about molarity!

• Molarity = moles/litres
• We can also find
• Litres = moles/Molarity
• mole = Molarity x Litres

How about an example? Your negative response has not been heard!

Consider the following equation: Ca(OH)2 + 2 HCL --> CaCl2 + 2H2O

How many litres of 0.100M HCL would be required to react completely with 5.00g of Calcium Hydroxide?

1) Write a balanced equation (it is already balanced)
2) Create a map that gets you from grams of Ca(OH)2 to litres of HCL 
3) 5.00g Ca(OH)2  x  1 mol Ca(OH)2  x   2 mol HCL  =  0.0135 moles HCL

                                     74.1g Ca(OH)2   1 mol Ca(OH)2  

4) Now use the molarity equation to find the amount of litres required

            Litres = 0.0135 moles HCL

                                       0.100M

             Litres = 0.135 L of 0.100M HCL        

Now how about the STP?

Consider the following equation: 2 H2 + O2 --> 2 H2O

Calculate the volume of oxygen gas required to burn 250.0L of Hydrogen gas at STP.

250.0L H2  x  1 mol  x  1 mol O2  x  22.4L   = 125.0L O2

                        22.4L      2 mol H2  1 mol O2

Here is a game to aid you on your quest to conquer the past!

For moles and stoichiometry!

Stoichiometry Part II

CHARLIE SHEEN WELCOMES YOU WITH A WITTY REMARK.

-insert funny remark countering greeting remark-

Stoichiometry

Pronounce stoichiometry as “stoy-kee-ah-met-tree,” if you want to sound like you know what you are talking about, or “stoyk:,” if you want to sound like a real geek.

Stoichiometry calculations involve particles, moles and mass. Yes, all readers. The lovely mole on your nose is back.

NOW LET US BEGIN OUR JOURNEY INTO STOYK:

Write a balanced equation

• you will need it for your mole ratio
• if you do not have a balanced equation you will be WRONG, and you don't want to be wrong

Create a 'road map'

• stating where you are starting and where you want to go
• many stoyk problems will follow this pattern:

grams(x) <--> moles(x) <--> moles(y) <--> grams(y)

• you can start anywhere along this map

Do the Calculations

• time to figure out the solution to your problem!

I believe an example is in order!

BAM, example presented:

I believe a different method of learning is in order as well!

BAM! interactive tutorial presented:

with lots and lots of clicking!

Are you feeling the stoyk? No? Re-read this post! and don't come back until you feel geeky enough to say stoyk.

JY

Stoichiometry

Stiochio --> element
Metry----> measurment

Therefore stoichiometry is the theoretical measurement of elements.
Now what is that supposed to mean?
Well, we can use stoichiometry to determine the amount of product a reaction will produce and vice versa.

First of all we need to look at the chemical equation we are using.
Eg. NH₃ + O₂ à H₂O + NO

Which now needs to be balanced correctly
Eg. 4NH₃ + 5O₂ à 6H₂O + 4NO

The coefficients serve as the mole ratio.
This means that when there are 4 moles of NH₃ and 5 moles of NO they will 6 moles of water and 4 moles of NO.

Now the fun part starts
Generally you will be given some amount of one of the reactants/products and have to figure out how much of  another molecule it will produce.
Using the mole ratios you multiply the amount you have by a fraction with what you are trying to find out on the top and the amount you already have on the bottom. This will give you the number of moles you are trying to figure out.

Eg. If you have 4.3 moles of NH₃ how many moles of H₂O will be produced?

4.3 Mol NH₃ x 6 Mol H₂O   = 6.4 Mol of H₂O
                        4 Mol NH₃
 Here is another example


This website is an excellent resource with tutorials and videos
http://www.chemcollective.org/stoich/reaction_stoi.php

Another example is provided in this video
http://www.khanacademy.org/video/stoichiometry-example-problem-1?playlist=Chemistry

Awwee Yeah Enthalpy Calculations Yeah ;)

So today, in class we learned about enthalpy calculations! Sounds scary right? But, naw! Its as easy as you can cry :) Here we gooooo............

To start off, lets define the key terms you will need to internalize!

Enthalpy: the "heat content" of a substance; in other words, the sum of kinetic and potential energy!

In an exothermic reaction, the enthalpy goes down, and it is converted into heat and released. 

In an endothermic reaction, the enthalpy goes up and it is absorbed.

To find the total change in enthalpy, you just subtract the reactant from the product. 

/\H = Hproduct - Hreactant 

Use this following picture as an example:

Where would you find the enthalpy in this diagram?

The location is labelled as C.

Find the enthalpy.

/\H = Hproduct - Hreactant 

/\H = 300 - 100 

/\H = 200 kJ

Example 2

If you had 3 moles of Carbon, and the energy produced per one mole -478KJ. Then how much energy is produced in total?

-478KJ X 3 moles = -1434KJ

 1 mole


^{Notice how the energy is negative; because it was produced, not absorbed}

I hope you guyss comprehend all this! GOOODLUCKKK!!

Chemical Reactions with Special Guest Energy Diagrams

Len Lesser, who hardly knew yee

I mean, after nine years Seinfeld, how could we?

I apologize. After Egypt, things have calmed down.

Not much mind blowing news today...

...unless IM hiding under a rock.

....then I need to read the news more.

Speaking of lesser...no, not the grammatical error. 

All chemical reactions involve changes in energy;

some release energy - exothermic

some absorb energy - endothermic

sound familiar? it should!

• exothermic reactions take less energy to break bonds than it gives off to form bonds
• endothermic reactions take more energy to break bonds than it gives off to form bonds

enthalpy (H) is the heat contained in the system

and with this information we can now begin our lesson on energy diagrams

• charts the potential energy changes from reactants to products

and with a chart always comes more information!

• Energy of Reactants (before hill)- total potential energy of all reactants in reaction
• Energy of Products (after hill) - total potential energy of all products in the reaction
• Energy of the Activated Complex (labeled transition state above) - the change in enthalpy in potential energy during reaction
• Activation Energy (energy of activated complex - energy of reactants) - energy that must be added to get reaction to progress
• change in enthalpy (ΔH) - change in enthalpy in potential energy during the reaction

and with information comes work!

• once ΔH is found ...
• ... you can write out an equations
• if ΔH  is negative than the energy is on the right side of the equation
• if ΔH is positive than the energy is on the left side of the equation

LOOK, A VIDEO LECTURE ON ENERGY DIAGRAMS! 

click it! CLICK IT NOW

The Lab To End All Labs

I KID.

BUT HEAD PROTECTION FOR OUR FRIENDS IN EGYPT! THEIR BULLETS CANNOT PIERCE YOUR COMPLEX CARBOHYDRATES

Speaking of bread, our lab has nothing to do with them!

Lab 5B: Types of Chemical Reactions

With this lab, we observe:

synthesis: A + B -> AB

decomposition: AB -> A + B

single replacement: AB + X -> A +XB (a metal with a metal, or a non-metal with a non-metal)

double replacement: AB +XY -> AY +XB

NOW, allow me to take you on an adventure through a lab with thrills, chills, and wow-we-have-a-lot-of-commas!

For those who were unable to be here on lab day, I suggest you read the following:

heated copper wires

Reaction 1

• Burning a copper wire with a bunsen burner

nail in copper sulphate

Reaction 2

• Placing an iron nail into Copper(II)Sulphate(L)

Reaction 3

• Heating some Copper(II)Sulphate(S)

Reaction 4

• Adding water to the heated Copper(II)Sulphate

Reaction 5

• Placing CalciumChloride(L) into SodiumCarbonate(L)

Reaction 6

• Placing mossy Zinc into hydrochloric acid

Reaction 7

• Adding Manganesse(IV)Oxide(S) into hydrogen peroxide(L)
• Test gas with glowing splint

Make sure you use any safety equipment necessary. If you have any appendages burned, clothes destroyed, or mind frazzled; I am not liable for any of it. ANY OF IT. 
Figure out which type of chemical reaction belongs to which reaction in this lab. As this is practice, and you should now have a better understanding of chemical reactions
Complete your lab report and hand it in. I recommend you hand it in for the betterment of your mind. Unless, you want to 'say no to the man', but there is no man. So you can't say no.

QUIZ TIME: Who Wants To Be A Millionaire Style!
and luck to all our Egyptian friends, who can say no to the man! 
dictatorship is going down!

Types of Reactions Continued

Last day we learned about 3 types of reactions: Synthesis, Decomposition and Single Replacement.
Today we learned the next 3 types of reactions: Double Replacement, Neutralization and Combustion

First let's look at double replacement reactions.
The general formula of double replacement reactions goes as follow:
AB + CD ---> AD + CB
Simply put it means that the metals or the non-metals trade places.
Eg. CaCl2 + Al2O3 ---> CaO + AlCl3


Of course this then has to be balanced
 Eg. 3CaCl2 + Al2O3 ---> 3CaO + 2AlCl3


However we need to be able to determine if a reactions is actually going to occur. To do so we must look at the "Table of Solubilities"

Using the table find the anion (negative ion) on the let and see if it is soluble or or not soluble. If it is not soluble the compound is a solid. If it is soluble the compound is aqueous.

Now what does this have to do with determining if a reaction is going to occur?
If at least one of the products has a change of state ie. aqueous to solid a reaction occurs
If no change of state happens no reaction happens.

Once you know a reaction is going to occur you need to make a net ionic equation. You only do this with reactions that actually occur!!!
You take reactants that make up the solid and use them on the left hand side of the equation (write their charges and numbers as well) and write the numbers of the solid product on the right hand side.

Eg. 4PO4  -3  (aq) + 3Ti +4 (aq) ---> Ti3(PO4)4


Combustion
Is a reaction where burning of air is involved.
General Formula:  AB + O2 ---> AO + BO
Eg. CH4 + 4O2 ---> CO2 + 2H2O


Neutralization
Is a reaction where and acid and alkali combine to form a salt and water
General Formula: HA + BOH ---> H2O + BA

Eg. 2HCl + Ca(OH)2 ---> H2O + CaCl2





A neutralization reaction is just a special double replacement reaction, therefore you need to make a net ionic equation as well.