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Topic: Combustion question and answer check please  (Read 5942 times)

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srchn4ansrs

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Combustion question and answer check please
« on: March 15, 2005, 08:31:53 PM »
First the combustion question.. During the combustion og 5.0 g of methanol (CH3OH) with O2, 27.2 kcal is released. Write a blanced equation for the combustion reaction (my answer = CH3OH + O2---->CO2 + H2O )... What is the change in enthalpy (my answer = DeltaH = -726.4 kJ) How many grams of methanol must be burned to raise the emp of 375.0 mL of water from 25 C to 95 C? (my answer = 4.8 g or 482.5 mg)

Second answer check... The activation energies for each of two reations were found to be 24 kJ and 53 kJ in identical temperatures which has the greates reaction and why? (my answer = 24 kJ has the greatest reaction due to the greater number of productive collisions of molecules in the lower activation energy (smaller hill to climb so-to-speak) as opposed to lessor number of productive collisions of molecules at 53 kJ activation energy.

Third answer check... Calculate the equillibrum constant.... H2 + I2== 2HI.... H2 I2 found to equal .86 mol/L and HI found to equal .27 mol/L (my answer to equillibrium constant K= .08)

Last one I promise.... For the reaction N2 + 3H2 == 2NH3 + 92kJ, in what direction will the equillibrium shift occur
If some NH3 is removed from mixture (my answer = forward (product side) shift
If Temp is increased (my answer = reverse reaction (reactant side)
If pressure is increased (my answer = forward reaction due to fewer # of moles of gas (product side)

Thank you to anyone who can help me with this. I am disabled and have missed a few classes and am really struggling with 12 total questions. I am doing my best to provide my own conclusions. Please do not think that I am asking for someone to do it all for me. I am just not certain of my answers. Thank you again.

Srchn
« Last Edit: March 18, 2005, 07:43:12 PM by srchn4ansrs »

Offline jdurg

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Re:Combustion question and answer check please
« Reply #1 on: March 16, 2005, 08:57:22 AM »
No problem.  We have no qualms about helping people out such as yourself when they show that they have attempted the problem first.  It's pretty easy to see that you've made an attempt to answer these questions, so now we can help you.   ;D

1):  For the reaction you have written, you have the formulas correct but the ratio is wrong.  On the left side you have 1C, 4H, and 3O.  On the right side, you have 1C, 2H, and 3O.  So the balancing is not correct.  You are short 2 H atoms on the right side.  

I'll have to get back to you later for the rest of these.  I'm posting this while here at work and some stuff just came in that I have to take care of so I have to jet.
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srchn4ansrs

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Re:Combustion question and answer check please
« Reply #2 on: March 16, 2005, 09:12:42 PM »
Thank you for your help so far... would I be able to correct the inbalance of (CH3OH + O2---->CO2 + H2O ) by making it CH3OH + O2 ---> CO2 + H4O or would the following be correct? CH3O2H + H2O2 ---> CO2 + 2h2O

I would very much appreciate any assistance on my questions posted in this reply as well as the original post. I am really stuck here. There are more questios that I have but I am still trying to work them and perhaps I'll post them later if it is OK. I just need more time with them. Thanks to all for any assistance.

Srchn
« Last Edit: March 16, 2005, 09:14:29 PM by srchn4ansrs »

Offline jdurg

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Re:Combustion question and answer check please
« Reply #3 on: March 16, 2005, 10:42:22 PM »
Your ideas won't work for balancing the equation because you are changing what the products and reactants are.  In order to balance an equation, you need to change the amount of products and reactants.  Here's an example.  Let's say you want to balance the reaction of calcium hydroxide + hydrochloric acid turns into water and calcium chloride.  The first step is to write out the reaction.

1)  Ca(OH)2 + HCl -> CaCl2 + H2O

The second step is totalling up the atoms on each side.

2)  Left: 1Ca, 3H, 2O, 1Cl.  Right:  1Ca, 2Cl, 2H, 1O.

So you can see that on the right side we are short one Hydrogen and one Oxygen, and we have one extra chlorine atom.  In order to balance this, we have to adjust the coefficients of the products and reactants we have listed.  So how can we add another chlorine atom to the left side?  By putting a 2 in front of HCl.  This gives:

3)  Ca(OH)2 + 2HCl -> CaCl2 + H2O.

Now if we retotal everything, we get Left:  1Ca, 4H, 2O, 2Cl.  Right:  1Ca, 2H, 1O, 2Cl.  We're almost balanced.  On the right side we're short 2H and 1O.  That's just one water molecule, so if we put a 2 in front of the H2O on the products side everything will be balanced.

Final)  Ca(OH)2 + 2HCl -> CaCl2 + 2H2O   ;D

Hopefully that will be of some help.  Sorry I can't get to the rest of them any sooner, but I've just been incredibly busy today.  :(
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srchn4ansrs

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Re:Combustion question and answer check please
« Reply #4 on: March 17, 2005, 01:16:28 AM »
JD,
Thanks for your help on this. However... I a still lost as to how to balance my 2 extra H on the left side without modifying the actual reaction that is occurring. In the problem I am adding O2 (oxygen) to Ch3OH (methanol) and when this occurs I do know that the product is Carbon Dioxide and water CO2 + H2O.

So... I cannot figure out how to get two additional H to the right side of the equation without alterring the chemical property itself which I now realize is what I had done in my first reply and attempt at balancing the equation. Worse yet is the fact that this is tep one in the question... aaaarrrrrgh! I feel like a 42 year old third grader!

My last gasp is this answer to the balancing question... 2CH3OH + 3O2---> 2CO2 + 4H2O

Thanks again for all your help. If anyone else would like to look at my original post and see if they could offer any assistance I would very much appreciate it. Thanks to all.

Srchn

I see AWK beat me to my conclusion. Thank you very much for your help. Any ideas on the rest of the original post? Thanks again.

Srchn
« Last Edit: March 17, 2005, 02:57:47 AM by srchn4ansrs »

Offline AWK

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Re:Combustion question and answer check please
« Reply #5 on: March 17, 2005, 02:46:38 AM »
2CH3OH + 3O2 = 2CO2 + 4H2O
generally:
CxHyOz + (x+y/4-z/2)O2 = xCO2 +  (y/2)H2O
AWK

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