- #1
Numeriprimi
- 138
- 0
Homework Statement
In a closed container with a volume of V = [STRIKE]5[/STRIKE] 50 l is a mixture of hydrogen and oxygen with the total mass m = 50 g. The container have pressure p = 300 000 Pa and the temperature t_1 = 20 ° C.
A) What is the number of moles n_1 (hydrogen) and n_2 (oxygen) in the container?
B) What heat Q is released after an electrical spark ignited the mixture? The calorific value of the hydrogen is 120 000 000 J / kg.
C) What is the pressure in the container when the temperature go down to t_2 = 100 ° C (after elektrical spark) and what is m_v weight of condensed water at this temperature?
... p_a = 1, 013 * 100 000 Pa; M_mhydrohen = 2,02/1000 kg/mol; M_moxygen = 32/1000 kg/mol; R = 8,31 J/(mol*K)
Homework Equations
A) pV = nRT
B) Q = Hm
C) p/T = const.
The Attempt at a Solution
A) pV = nRT = m/M_m * RT; m/V = pM_m/ RT; m/V(hydrogen) = pM_mhydrogen/RT; V_(oxygen) = pM_moxygen/RT
The system of equations:
- V_hydrogen +V_oxygen = V (V_oxygen = V - V_hydrogen ... substituted into the second equation)
- V_hydrogen*(p*M_mhydrogen/RT) + V_oxygen*(p*M_moxygen/RT) = m
Ok, I solve the system of equation... And I get V_oxygen = 0,01 m^3; V_hydrogen = 0, 04 m^3
Now back to equation pV = nRT; n = pV/2RT (2 because it H_2 and O_2, it is right?)
And I get n_oxygen = 0, 626 mol; n_hydrogen = 2, 45 mol
It is OK?
B) Q = Hm = H*n*M_mhydrogen*2 (2 because it is H_2, it is right?)
Q = 1 187 760 J... It is OK?
C) Hmmm... And this is the biggest problem.
It is isochoric progress? Than p_1/T_1 = p_2/T_2; p_2 = p_1*T_2/T_1
p_2 = 300 000 * (273,15 + 100)/(273, 15 + 20) Pa = 381 867 Pa
Condensed water... Hmm, basic assumption is that the system is in steady state - System of saturated steam and liquid. Saturated steam is not an ideal gas ... The equation p / T = const. ist probably wrong. I really don't know any equation for saturated steam... Can you help me?
Thank you and sorry for my bad English :-)
Last edited by a moderator: