Monday, February 21, 2011

February 21, 2011

Energy Calculations

As an extended lesson from last lecture about EXOTHERMIC and ENDOTHERMIC reactions, we discovered more functions of the "H"-which is the heat contained in a reaction or the energy change of a reaction, expressed in KJ/mole.

Where is it on the Balanced Equation of a reaction?

EXO:  I2     +       Br2       -> 2IBr + 81.5 KJ
END:  I2 + Br2 + 81.5KJ -> 2IBr

Today, we learned that Delta H can also be the used to convert from Energy to Mole!
Thus, MOLE is back once again...DAWN...DAWN...DAWN..
The Conversion Factor varies for EVERY REACTION!

How to determine the Conversion Factor?

Example 1.

in Exothermic reaction, KJ, the energy, the Delta H is on the right side.
For Conversion Factor to Mole, express the Delta H, which is (-393.5 KJ) over the Coefficient # of mole of a compound in a Balanced Equation.
So, there are 2 things you are looking for:
1. the KJ -if Exo, then "-", if Endo, then "+"
2. the Coefficient

In this case, it is -393.5 KJ/ 1mole of Carbon or O2, or CO2.

The value of Delta H depends on which chemical you are referring to, therefore, it is not a constant!!

Example Questions:

1. Calculate the energy released when 0.25 moles of  CO2 is produced?

CH4 + 2O2 -> CO2 + 2H2O + 612 KJ

Solution: 0.25 mol CO2 x -612KJ/1 mol CO2 = -153KJ  or 153 KJ energy released
* the Negative sign = energy released, put either

Now we can calculate from energy to moles!

2. How many moles of O2 is needed to produce 2300 KJ of energy?
 Produce = "-"

Solution:- 2300 KJ x 2mol O2/-612 KJ = -7.6mol of  O2.

Are ready for More Challenge?
Practice Questions Set
1.Calculate the energy released when 2.7 moles NH3 is reacted?

4 NH3 + 5 O2 -> 6 H2) + NO + 905 KJ

2. Calculate the number of grams of Oxygen gas (O2) that would be required to produce 5500 KJ of energy.(use the MOLE MAP for HELP!)

CH4 + 2O2 -> CO2 + H2O + 890.3 KJ

Magnesium burning in air = Exothermic Reaction!

 video of Exothermic Reaction Demo

Friday, February 18, 2011

February 16, 2011

Today in class we learned a couple of new things. But before I explain to you what we learned let me just quickly tell you what we got back and what is for homework.

What We Got Back:
- Virtual Lab
- Lab:5B
Quiz; (Is Coming Back Next Class)

- Worksheet; Calculations with exothermic and endothermic reactions

Now for what we learned in class was endothermic reactions, exothermic reactions, and energy diagrams.

Endothermic Reactions + Exothermic Reactions:
You are probably thinking, "well first of all what the heck are these 'reactions'?" and "what is the difference between them?" Well don't worry because these two are actually quite simple to learn! Here are some definitions, facts and examples...........
- definition of endothermic reaction =
a chemical reaction accompanied by the absorption of heat.
- definition of exothermic reaction =
a chemical reaction accompanied by the release of heat.
- add energy to break bonds and gives off to join together
- more energy than it gives off to form bonds = endothermic
- less energy than it gives off to form bonds = exothermic
- enthalpy (H) = the heat contained in the system
- examples of endothermic reactions = cooking an egg, baking bread, melting ice cubes, evaporating liquid water, splitting a gas molecule, mixing water and ammonium nitrate, and producing sugar by photosynthesis.
- examples of exothermic reactions = all combustion reactions (fires), explosions, making ice cubes, formation of snow in clouds, a candle flame, rusting iron, burning sugar, and nuclear fission.

Energy Diagrams:
- definition = a graph of the energy of a reaction against the process of the reaction.
- Energy of activated complex; potential energy of the transition state betweeen reactants and products.
- Activation Energy; the energy that must be added to get the reaction to progress.
- /\H; the change in potential energy during the reaction.
- Example of an endothermic energy diagram with terms (down below):

- Can you figure out where the terms belong ?!?!?! Without looking above!!!!! 

- Example of an exothermic energy diagram with terms (down below):

- Can you figure out where the terms belong ?!?!?! Without looking above!!!!! 

Energy in Equations:
- exothermic reactions have the energy on the right and a negative /\H
- endothermic reactions have the energy on the left and a postive /\H
example = CH4 + 2O2 g CO2 + H2O
                Higher Energy    Lower Energy

Whewww, alot of information but with practice and patience you can master it! :) Now for the rest of this entry I am going to give you some youtube videos, worksheets, images doing with endothermic vs. exothermic, and then for your treat you get crosswords! Yay!


Worksheets + Information:

Images: (Guess which are Exothermic or Endothermic!!!!)


Tuesday, February 8, 2011

February 8th, 2011

as the name infers, this type of reaction occurs between two different compounds.
the new compound forms by exchanging atoms or groups-"swap" partners!

AB + CD -> CB + AD

     ======> [AgNO 3 + NaCl -> AgCl + NaNO 3] <======

Here are some practices:
NaCl + H2SO4 -> ___________________
Ba(NO3)2 + Na2SO4 -> _______________

what you are looking for is two COMPOUND reacting!

How to determine if a DR actually occured?
reactant changes state during the reation = there is reaction
no change of state = no reaction

How to determine the states?
use [Table of Solubilities]: aq or s
1. find anion in the left hand column
2. look for cation in 2nd column
3.follow its presence or absence to the word "soluble or not soluble"
4.if soluble, compound is aq
5.if insoluble, the compound is s

Writing a NET equation
When you have a precipitation, there is a NET equation
key: aq ions that are the same on both sides get cancelled

2Na3PO4 (aq) + Ca9NO3)2 (aq) -> 6NaNO3 (aq) + Ca3(PO4)2 (S)
NET equation: 3Ca 2+ (aq) + 2 PO4 3- (aq) -> Ca3(PO4)2 (s)

a special DR where acid react with bases to produce water and an ionic salt!
2HBr + Sr(OH)2 -> SrBr2 + 2H2O

involves chemicals to be burned and oxygen.
AB + O2 -> AO + BO
==========>[C4H8 + 6O2 -> 4CO2 + 4 H2O]<=========

1. AgNO3(aq) + K2CO3(aq) -----> 

 2. Al(OH)3 + H2SO4(aq)

3.  Ba3(PO4)2(aq) + K2CO3(aq)

4. HCl + NaOH

5. 2HCl + Mg

That's all for today's CHEM lesson.
---Thanks for reading ---

WHAT TYPE of REACTION is THIS??  just for pure fun

Friday, February 4, 2011

February 4, 2011

Lab 5B

Today in class we did Lab 5B!!! This lab was all about the different types of Chemical Reactions. Here is a detailed summary of the lab......

- In this experiment, you will first observe examples of each of the four types of chemical reactions (synthesis, decomposition, single replacement, double replacement). Next, you will write chemical equations that support your observations. Finally, you will classify each reaction as synthesis, decomposition, single replacement, or double replacement.

- to observe a variety of chemical reactions
- to interpret and explain observations with balanced chemical equations
- to classify each reaction as one of the four main types (mentioned above)

Procedure (What We Did):
*For every reaction we made observations before, during, & after in our Table 1.

- Reaction One;
1. We adjusted our bunsen burner to medium/high heat.
2. Using crucible tongs, we then held a 6cm length of copper wire in the hottest part of the flame which is the bottom of the flame (the colour is blue) for a few minutes. 

- Reaction Two;
1. For this reaction we first cleaned an iron nail with a piece of steel wool so that the surface was nice and shiny. 
2. Then we placed the nail in a test tube and added coppper (II) sulfate solution so that one half of the nail was covered.
3. After 15 minutes, we removed the nail and took down the observations.

- Reaction Three;
1. In a test tube we put solid copper (II) sulfate pentahydrate about one third full.
2. Using a test tube clamp, we held the test tube in the bunsen burner flame taking down observations.

- Reaction Four;
1. We let the contents from Reaction Three cool down.
2. Using a medicine dropper, we added two to three drops of water in the test tube.

- Reaction Five;
1. We filled a test tube with calcium chloride solution. Then filled another test tube with sodium carbonate solution.
2. Then we poured the calcium chloride solution into the test tube containing sodium carbonate solution. We basically mixed them together into one test tube.

- Reaction Six;
1. We placed a piece of mossy zinc in a test tube.
2. Then we added hydrochloric acid solution to the test tube until the mossy zinc was completely covered.

- Reaction Seven;
1. Filled a test tube with hydrogen peroxide solution.
2. Then we added a small amount of manganese (IV) oxide. The manganese (IV) oxide acted as a catalyst in this reaction.
3. Then we placed a glowing (not burning) splint into the mouth of the test tube.

*Lastly, but not least, we cleaned up the lab and wahed our hands! :)

- We did not have any time left in class to do the follow up questions and analysis of resulsts but we will do that during next class. And that was the end to our lab......

For Next Class:
- the homework for next class is to finish that online worksheet we were doing two classes ago. Remember we had to follow that activity online and answer questions about that on this worksheet.... well I hope you remember    :o   :D

Now for the fun + exciting extras!!!
* youtube:

* images:

Thursday, February 3, 2011

February 3, 2011

Virtual Lab!

- During yesterday's class we went to the computer lab to work on a virtual lab! This virtual lab was about testing different components together and observing their changes. Each reaction was different and each had different characteristics between each other. During this virtual lab we took down our notes on a worksheet which we hand in next class. If you didn't finish the lab don't worry about it because we are able to bring it home to hand in next class.

- For Next Class:
Prepare Lab 5B as we are doing that lab tomorrow in class.
Finish worksheet: "WS 5.6 Types of Reactions".

- Dates to Remember
February 10, 2011: Quiz on translating word equations, balancing equations, types of reactions (including predicting products and solubility)
February 16, 2011: Lab 5B Quiz
February 25, 2011: Chapter 5 Test

- Youtube Videos (Very Helpful, Trust Me :)

- Other Worksheets (Also Very Helpful, Trust Me :)

Wednesday, February 2, 2011

February 2nd

Last time, our friends Oxygen and Sodium demonstrated Synthesis, Decomposition, and Single Replacement with you. But did you know that there are three more reaction types still untouched on?


Double replacement is when two compounds swap positive ions to create two whole new products.


4Rb3PO4(aq) + 3Ti(NO3)4(aq) ----> 12RbNO3(aq) + Ti3(PO4)4(s)

2NH4I(aq) + MgSO4(aq) ---->  (NH4)2SO4(aq) + MgI2(aq)

The general form for double replacement reactions is AB + CD --> CB + AD.


Combustion happens when substances burn in the air to produce carbon dioxide.


C10H8 + 12 O2 ----> 10 CO2 + 4 H2O

2C3H6 + 9O2 ----> 6CO2 + 6H2O

The general form for combustion reactions is AB + O2 --> AO + BO.


Neutralization is a reaction in which an acid is combined with a base to produce water and a salt.

2HCl (aq) + Ca(OH)2 (aq) ----> 2H2O(aq) + CaCl2(l)

HCl + NaOH ----> NaCl + H2O

The general form for a neutralization reaction is HA + BOH --> H2O + BA.