Bond Energies

Bond energies require knowledge of molecular structure
O2: O=O     N2: - has a triple bond (still need to figure a few symbols out)

Formation reactions: produce one mole of product from elements in their standard state
-remember HOFBrINCl & the making one mole of product
Na(s) + 1/2 H2(g) + C(s) + 3/2 O2(g) --> NaHCO3(s)

Last but not least when calculating a reaction's enthalpy change (H):
Bonds broken - bonds formed
              (reactants)                             (products)
Yes, it is the reverse of the other calculations.

Please note that H (enthalpy change) is not the same as Hx (molar enthalpy change)
One more thing before wrapping up. Consider the generic reaction:

2A  +  B  -->  A2B  H = -300kJ

molar enthalpy of A: HA = -150kJ/mol 
molar enthalpy of B: HB = -300kJ/mol
[That is all for today. Question: What is the name of the molecule bunny-O-bunny? Answer: An ether bunny  Question: What is a cation afraid of? Answer: A dogion.]

Hess’s Law and Hof [aka heats of formation]
**technical difficulties abound with little delta symbols and superscripts and subscripts - do you know how to include symbols, superscripts and/or subscripts?



With Hess’s law – use each of the given equations, add to arrive at the target equation
-if the equation is reversed, the sign of H is also reversed (+ to – and/or – to +)
-if the equation is multiplied by a value, multiply H by the same value

One more thing, consider the equation written below:

4CO2 (g) + 6 H2O(g) -->2 C2H6 (g) + 7 O2 (g)            H = 849.0KJ

the molar enthalpy of CO2: HCO2 = 212.25 kJ/mol        [849kJ / 4 mol]

Any equation can be interpreted per mole of any substance in the equation

Heats of Formation Hof

-be able to write the formation reaction for any substance [produce one mole of product from elements in their standard state]

-when calculating H with heats of formation (data tbl 799-800) remember that it is:

                 (products) – (reactants)

For a small change a few elephant jokes. Ready or not, here they come. Q: How do elephants communicate? [On the elephone.]  Q: Why are elephants large, grey and wrinkled? [Have you ever tried ironing one?]  What time is it when an elephant sits on your fence? [Time to get a new fence.]

Day 4 - Food Snackfood Burning

A few snackfood burning lab write-up tidbits:
-word processed - [use a decent sized font - please :<)]
-include a copy (real or reasonable reproduction) of the nutrition label
-follow along with the calculations as outlined on the assignment handout (hint, hint - using p320 #4(eicosane) as a guide for several aspects of the calculation - Did you read the posting from Day 3?)
-include the assignment sheet (its green) with the final submission
-joules to food calories (Cal as opposed to cal)
http://health.howstuffworks.com/health-illness/wellness/physical-fitness/weight-loss/calorie1.htm

Additional items to include
-include a cheesy joke in the footer (optional - but appreciated)

This colour of font was selected because of the cheesy nature of the following joke. Two antennas met on a roof, fell in love and got married. The ceremony wasn't much, but the reception was excellent.  [In this age of digital/satellite cable, this joke is definitely from another era. If in doubt about its humour, share it with the parental figures. :<]

Energy Day 3 - Representing Enthalpy Change

Four ways to represent enthalpy changes are to be considered.
-see the four ways outlined on page 319 of Nelson Chemistry 12

A nice review of thermochemical equations is found at"
http://chemistry.about.com/od/physicalchemistrythermo/a/thermochemlaws.htm

This next link has some questions with answers - available after you answer the question. The answer does not require units, but include a negative sign if required. One other tidbit for the questions, you need to ensure that you have calculated the molar enthalpy of the substance of interest. [That is, you may need to divide the stated enthalpy of the equation by the moles (coefficient) associated with the desired reactant.]
http://chemistry.csudh.edu/lechelpcs/thermoequationscsn7.html

From today: Page 319-320 [2,3,4,5]  and page 320 [1 to 4]

A helpful hint for #4 page 320 (the eicosane question), the surroundings that are heated as a result of the burning candle are the copper container and the water in the copper container.
So -      nH combustion eicosane = -[mcTwater  +  mcTcopper]   ...once again, 'delta' represented by 

One other thing with this question - in (d) a percentage error calculation is requested - consider the %difference calculation outlined on page 778 of Nelson Chemistry 12. [% difference/ % error - the calculation will work for both. In this case the predicted value = actual value = -13.3 MJ  ...watch the units]

Now should you have to use a similar approach with a 'tin can' (~ iron) and a burning cheesie/chip/marshmallow/peanut/cracker......all the better. :<)

A few closing thoughts in honour of the potential cheesie burn - some cheesie jokes: (1) What do you call a fish with no eyes? A fsh  (2) I went to buy some camouflage trousers the other day but I couldn't find any.   (3) And finally, there was the person who sent twenty different puns to his friends, with the hope that at least ten of the puns would make them laugh.     No pun in ten did.

Day 2 of Energy - Enthalpy & Molar Enthalpy

-once again, no 'delta' symbol appears - for now it is just a 
(I haven't figured out the delta symbol part yet :<(

Two equations to consider

(1) H = nHx     or  (2) nHx = -mcT

where n - moles of system substance;   Hx  - molar enthlapy;    H  - enthalpy/ heat


If the question mentions the surroundings
- typically water (or a water-based solution, like a dilute acid or dilute base)
-surrounding information - amount of solution (volume, mass), temperature change info about surroundings
Then use the second equation [nHx = -mcT]
-when working with the mcT portion of the equation, make sure that mass (m) and the heat capacity (c) and the temperature change (T) are all for the same substance (the surroundings)


If the surroundings are not mentioned
-use the first equation



Other tidbits to consider
-the question may ask for or provide mass - convert to moles (n)

From today:
Do the following questions. Use proper form with your solutions.

Page 308 # 2 and Page 312 #1ab & 4** [H = nHx or nHx = -mcT]*
Page 310 – 4 & 5 and Page 312- 2, 3, 5
*where the H = 'delta'H
**don't let p312 #4 confuse you, the temperature mentioned is meant to mislead you, did it?

Day 1 of Energy q=mct

- did a little bit of q = mc 'delta't
the mathematical calculations involve heat energy, but there is no acknowledge as to the origin of the energy - that will change - and soon
-terms, terms, terms.....
-system - the actual reaction
-surroundings - environment in which the reaction occured, typically water
-why water" (1) readily available (2) flows easily (3) high specific heat capacity - absorbs heat without experiencing a great temperature change (unlike some metals for example)
-when working with any dilute solution surroundings - assume that it has the same heat and density properties as pure water (c=4.18 J/gC, D = 1g/mL)

Energy Unit Ouline

• calculating enthalpy change q=mct
• molar enthalpy calculations – comparing system and surroundings
                o nHx = H and nHx=-mct [Could not get the 'delta' symbol]
• 4 ways to represent enthalpy changes
A few methods to determine the energy change associated with a chemical reaction
• Method 1: Hess’s Law – add up some equations then add up the enthalpy change of each equation
• Method 2: Standard Enthalpies of Formation – using tabulated data
• Method 3: Bond energies – using still more tabulated data, this time: [bonds broken – bonds formed]
• Entropy – will a reaction tend to be spontaneous?
• Measuring Rates of Reactions – graphically and given experimental data & a balanced chemical equation
• factors Affecting Rates of Reactions
• Rate Laws
• Potential Energy Diagrams
• Collision Theory
• Mechanisms