January 25, 2015

Homework Help: Chem.

Posted by Christopher on Monday, January 29, 2007 at 6:39pm.

Nitrogen oxide (NO) has been found to be a key component in the many biological processes. It also can react with oxygen to give the brown gas NO2. When one mole of NO reacts with oxygen, 57.0 kJ of heat is evolved.
a) Write the thermochemical equation for the reaction between one mole of nitrogen oxide and oxygen.
Is a thermochemical equation just like any other equation? I have written:
2NO + O2 --> 2NO2
b)Is the reaction exothermic or endothermic?
I know what endothermic and exothermic reactions are, but how do I determine this from the information given?
d) What is delta-H when 5.00 g of NO reacts?

What I had is this:
5.00 g x 1 mol/30.01 g = .1666 mol
1/.1666= 6.00
delta-H= q
q= 57.0 kj/mol / 6.00 = 9.50 kJ

I'm not sure if this makes sense or not.
e) How many grams of nitrogen oxide must react with an excess of oxygen to liberate ten kilojoules of heat?
This sounds a bit like a limiting-excess reaction to me, but I'm not sure if I need to use that to complete the problem. So far I have written
10.00 kJ = m * Cp * delta-T
However this leaves me with two unknowns, so that's not a big help.

a) Yes and no. A thermo equation is just like any other equation EXCEPT that they are written for 1 mol of the material. Besides, the problem states to use 1 mol NO.
NO + 1/2 O2 ==> NO2
Thermochemists aren't bothered by the 1/2 O2.

b)The problem states that 57.0 kJ of energy is EVOLVED (hint: given off?). So that makes it an __________ reaction.

c)You are correct with the number but is the sign correct? If heat is given off then delta H should be negative?

d. 30.01 g NO will react to give 57.0 kJ of heat. So how many g NO are required to give 10 kJ of heat?
30.01 g NO x 10 kJ/57.0 kJ = ??

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