Confused about Physical Chemistry Calculations?

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Discussion Overview

The discussion revolves around physical chemistry calculations, specifically focusing on stoichiometry, molar relationships, and the determination of molecular weights. Participants pose questions about specific problems related to the combustion of a fuel, the calculation of moles in various contexts, and the determination of relative molecular mass for compounds.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Exploratory

Main Points Raised

  • One participant queries the mass of dinitrogen tetroxide (N2O4) required to oxidize 322 kg of liquid fuel (CH3NHNH2) and expresses uncertainty about their calculations, suggesting they arrived at 805 kg while the expected answer is 875 kg.
  • Another participant asks for the balanced reaction and the calculation of moles for the given fuel, indicating that understanding these steps is crucial for solving the problem.
  • A different participant provides the balanced equation for the reaction and suggests a method for calculating the mass of N2O4 needed, emphasizing the importance of molecular weights.
  • Participants discuss the calculation of moles for various substances, including chlorine gas and hydrogen gas, with one participant noting the relationship between moles and the number of particles.
  • Questions are raised about the rationale for using carbon-12 as a standard for relative atomic mass, with one participant suggesting availability and transport ease as reasons.
  • Another participant presents a problem involving the calculation of the relative molecular mass of hemoglobin based on the amount of iron it contains, expressing confusion over their results compared to expected values.
  • Participants explore the volume of steam produced from heating ice, with calculations involving the ideal gas law and expressing uncertainty about the results obtained.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the calculations presented, as multiple views and uncertainties are expressed regarding the correct answers and methodologies for solving the problems.

Contextual Notes

Some calculations depend on the accurate determination of molecular weights, which are not provided in the discussion. Additionally, assumptions regarding the ideal behavior of gases and the specific conditions of the problems are not fully detailed.

siewwen168
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Hello,there are some question about physical chemistry to be asked. :-p

1) The space vehicle,Gemini,started its journey in space with 322kg of liquid
fuel, CH3NHNH2. This fuel is oxidised by dinitrogen tetroxide,N2O4,to form
nitrogen,carbon dioxide and water.hat is the mass of N2O4,in kg,that is
required to oxidiese all the fuel?
(A) 258
(B) 644
(C) 805
(D) 875 *
(E) 161
The answer i got is c,but actual is d,is there anything wrong bout my calculations??can anyone show me? :smile:

2) Which of the following contains 1 mol of the particles stated?
(A) Chlorine molecules in 35.5g of chlorine gas
(B) Electrons in 1g of hydrogen gas *
(C) Hydrogen ions in 1dm3 of 1 moldm-3 aqueous sulphuric acid
(D) Oxygen atoms in 22.4dm3 of oxygen gas at s.t.p

thanks a lot for anyone who help :wink: :smile: :-p
 
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The space vehicle,Gemini,started its journey in space with 322kg of liquid CH3NHNH2

How many moles is this?


can you write out the balanced reaction that is taking place? Do these 2 steps and you should be able to get the answer. If not post what work you have done.

2) Which of the following contains 1 mol of the particles stated?

Once again calculate moles.

For A how many moles is 35.5g of Cl2 gas? 1 mole of Cl2 has 2 moles of Cl molecules.
b) how many moles is 1g of H2 gas? there are 2 e- in 1 mol of H2 gas...
etc...
 
hi,actually from my calculation of the first question,the mass of N2O4 that i got is 805kg,but the answer given is 875kg.i don;t think that i have anything wrong in my calculations,so i need your answer.Because those question got a lot of mistakes,haha,maybe I'm just lying to myself.but pls,can u give me your answer?

Before i proceed,i have to apologize first because i got more question to trouble u.so sorry bout that. :blushing: :smile:
1) Explain why carbon-12 replaced oxygen as a standard in the determination of relative atomic mass?(or why it used as a standard in determining Ar?)
Is it because carbon-12 is more available compared to oxygen,and it's easier to transport than oxygen.this is my answer,but i don;t know whether correct or not.it sounds stupid,right? :-p

2) Haemoglobin is a protein which carries oxygen in the red blood cell. Each
molecule of haemoglobin contains 4 iron atoms.If 1g of haemoglobin contains 0.00341g of iron ,calculate the RMM of haemoglobin.

3) The density of ice is 1.00gcm-3.What volume of steam is produced when 1cm3 of ice is heated to 323degree celsius(596K) at a pressure of 1 atm.(101kPa)? (1 mol gas occupies 24.0dm3 at 25 degree celsius and 1 atm.)

Till here,that's all. I think there are more.sorry for that.u may think that i;m lazy to solve my own problem,but i did try,at last,i can't get it.therefore,i need someone to help.anyway,thanks a lot for your help. :-p :smile: :wink:
 
The balanced equation is:
CH3NHNH2 +(5/4)N204-----> (9/4)N2+CO2+3H20
I don't have a periodic table so you have to plug in what the values are...

322kg fuel x (1000gfuel/1kgfuel) x (1 mol fuel/mw of fuel) x (5/4 mol N204/1mol fuel) x (mw of N204/1mol N204)= units cancel and you get your answer in g of N204, you just need to fill in the 2 molecular weights. The answer asks for amount of N204 in kgs so just divide your answer by 1000
 
These are all the same types of problems

1) instead of me typing this website explains-http://dl.clackamas.cc.or.us/ch104-03/changes.htm

2.)It says the ratio of molecules of Fe to a molecule of hemoglobin is 4:1. How many moles of Fe is 0.00341g of iron? Divide this by 4 and you have the number of moles of hemoglobin. Thus you know 1g is X moles of hemoglobin from that you should be able to find mw of hemoglobin

3.) how many moles of water is 1cm^3 of ice? figure that out and use PV=nRT
 
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question again.

thanks bout the answer for changes in standard. :smile:

for second question ,0.00341g of iron have 0.00341/26 moles of iron atoms ,right?the answer will then divided by 4 because 1 molecule of haemoglobin contain 4 atoms of iron.1g of haemoglobin will contain the moles that i count,then 1g will be divided by the answer,and the relative molecular mass of haemoglobin will be known.i got 30498.5 but the answer is 65454,why? :confused:

For the third question, 1 cm^3 of ice is 1/18 mole of ice,right?Then,pV=nRT,
V=nRT/p
=(8.31x1/18x596)/(101x10^3)
=2.72x10^-3 m3
*the answer given is 2.67 dm3,when i convert my answer,it's wrong ,why? :redface:

anyway,thanks a lot for helping me so much :-p :wink:
 

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