Some General Chemistry Questions
July 5th, 2021
A 6.55g sample of aniline (C6H5NH2, molar mass = 93.13g/mol) was combusted in a bomb calorimeter with a heat capacity of 14.25kJ/C. If the initial temp. was 32.9C, use the information below to determine the value of the final temperature of the calorimeter.
4 C6H5NH2 + 35 O2 —>24 CO2 + 14 H2 + 4 NO2
Delta Hrxn = -1.28 x 10^4 kJ
I believe I would begin here by using Qcal=Ccal x Change in T, which would be:
Qcal= 14.25kJ/C x (32.9X – T2)
qcal is the opposite of qrxn which is the same as Hrxn if I’m correct.
So then it would be:
1.28 x 10^4 = 14.25kj/C x (32.9C – T2)
Solve for T2? But, what comes out as wrong to me is why would I be given 6.55g and the molar mass if I wouldn’t use it. So I’m lost here. any help?
Question 2:
The value for DeltaH for the reaction below is -126kJ. The amount of heat that is released by the reaction of 25.0g of Na2O2 with H2O is _____kJ.
2 Na2O2 + 2 H2O —> 4 NaOH + O2
Not a clue here.
Question 3:
For which of the following reaction is the value of DeltaHrxn equal to DeltaHf for the product?
a) 2 H2 + O2 —> 2 H20(g)
b) 2 C + 2 H2 —> C2H4(g)
c) N2 + O2 —> 2 NO(g)
d) 2 H2 + O2 —> 2 H2O(l)
e) H2O + 1/2 O2 —> H2O2(l)
NEED CONFIRMATION ON ANSWER TO THIS ONE:
Determine the mass of H2O formed when 12.5L NH3 (at 298K and 1.5atm) is reacted with 18.9L of O2 (at 323K and 1.1atm.)
Answer = 37.84g of H2O
I basically just first used Ideal Gas Law to determine moles of both NH3 and O2.
Then used them to find how many moles of H2O each produced. Then combined the moles of H2O produced by each for total moles of H2O. Then used molar mass to convert to grams of H2O and arrived at that number. Is this correct?
Sorry for such a long post, but I felt it better to put them all in one post, rather than flood the forum with 4 different posts.
your equation makes my head hurt, wow its been a while since I did chemistry. But sorry matte cant help ya. hopefully someone else can.
question 2 – use the fact that delta H gives the heat produced when 1 mole of the compound is formed from its elements in their standard states.
So find out the limiting reagent, evaluate the no of moles, and multiply that by delta h to get the answer.