Feb 21 - Enthalpy Calculations

H : Energy change in the reaction. Units - kJ/mole

Eg.  CH₄ + 2O₂  -->  CO₂ + 2H₂O  + 812kJ

H can be expressed as:

-812kJ/1mole CH₄ or -812kJ/2mole O₂ = -406kJ/1mole O₂

-812kJ/1mole CO₂ or -812kJ/2mole H₂O = -406kJ/1mole H₂O

Ex. calculate the energy released when 0.35 moles of  H₂O is produced

0.35 moles H₂O * (-406kJ/1mole H₂O) = -142.1kJ

                             2Sig Fig                    = -140kJ

Ex. How many moles of CH₄ are needed to produce 2100kJ of energy?

2100kJ * (1mole CH₄/-812kJ) = -2.586

                                                = -2.6

                                                is  2.6 since mole cannot be negative

Link to Enthalpy Calculation : http://www.saskschools.ca/curr_content/chem30/modules/module3/lesson3/lesson3.htm

Feb16, Exothermic and Endothermic

Exothermic- a reaction where it realeases energy to the surroundings
Endothermic- a reaction where it absorbs energy from the surroundings


-Molecules held together by chemical bonds
          -Add energy to break bonds
          -Give off energy to join together

Endothermic- reaction takes more energy to break bonds than it gives off to form bonds

Exothermic - reaction takes less energy to break bonds than it gives off to form bonds

Enthalpy which has a symbol H and a unit joules, is the heat contained in the system

Energy Diagrams

-Chart the potential energy of the chemicals as they change from reactants to products

-Reactants start with certain amount of energy. Energy is added to start the reaction and then nergy is released as reaction proceeds

-The relative amounts of energy determine if a reaction is endothermic or exothermic

Endothermic-





Exothermic-

1. Energy of reactans = total potential energy of all reactants in the reaction

2. Energy of products = total potential energy of all products in the reaction

3. Energy of the activated complex = potential energy of the "transition state" between reactants and products

4. Activation energy = the energy that must be added to get the reaction to progess (reactants to activated complex)

5. ΔH (change in enthalpy) = the change in potential energy during the reaction. It is the energy of products

 - energy of reactants

Energy in Equation

-Exothermic reactions have energy term on right hand side and a negative ΔH

Eg.  CH₄ + 2O₂  -->  CO₂ + 2H₂O  + 812kJ

                                                           (ΔH)

Endothermic reactions have the energy term on the left hand side and positive ΔH

Videos that's helpful and entertaining

Links that might help : http://www.emsb.qc.ca/laurenhill/science/exo.html

February 4 - Lab 5B

So today we did lab 5b, which had to do with chemical reactions.

The 4 main chemical reactions that were observed in this lab were synthesis, decomposition, single replacement, and double replacement.

The purpose of the lab was to :

1. observe a variety of chemical reactions
2. interpret and explain observations with balanced chemical equations
3. to classify each reaction as one of the four main types

So in this lab, we did seven different experiments, and each one would be classified as a synthesis, decomposition, single replacement, or double replacement reaction.  

Reaction 1: burning a copper wire.

Reaction 2: putting an iron nail in copper (II) sulfate solution.

Reaction 3: heating up copper (II) sulfate pentahydrate in a test tube.

Reaction 4: add water to product of reaction 3.

Reaction 5: combine calcium chloride with sodium carbonate.

Reaction 6: put mossy zinc into hydrochoric acid solution.

Reaction 7: mix hydrogen peroxide solution with manganese (IV) oxide.  Then put glowing splint of wood into mouth of test tube.

February 2 - Chemical Reactions Cont'd

We learned about the rest of the chemical reactions today which were: Double Replacement, Combustion, and Neutralization.


Double displacement: This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. These reactions are in the general form: AB + CD ---> AD + CB

One example of a double displacement reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate:

Pb(NO₃)₂ + 2 KI ---> PbI₂ + 2 KNO₃

Combustion: A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat:
AB + O2  --> AO + BO

An example of this kind of reaction is the burning of napthalene:

C₁₀H₈ + 12 O₂ ---> 10 CO₂ + 4 H₂O

Acid-base: This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H⁺ ion in the acid reacts with the OH^- ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water:            HA + BOH ---> H₂O + BA

One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide:HBr + NaOH ---> NaBr + H₂O


1)  Does your reaction have oxygen as one of it's reactants and carbon dioxide and water as products? If yes, then it's a combustion reaction
2) Does your reaction have water as one of the products? If yes, then it's an acid-base reaction
3) If you haven't answered "yes" to any of the questions, then you've got a double displacement reaction

Vids have low volume so turn it up a bit

Links that might help http://www.visionlearning.com/library/module_viewer.php?mid=54