Gas law, how to fine the final T and Final P?

[nevada2012]

i don’t understand how they got this answer

can you please explain the steps
needed to fine the Final T and How the final P was found.
thanks


N2H4 + 3O2 ==> 2NO2 + 2H2O


assume there are 60 moles of O2, what is the final T and P

V = 20L
T1 = 290K
n (N2H4) = 20
Cp = 57 kJ/C
Hc = 194.1 x 105 J/kg


final T:
20 mol N2H4 * 32g N2H4 / 1mol N2H4 * 1kg / 1000g =0.640 kg N2H4

0.640kg N2H4 * 194.1 * 10^5 J/ Kg N2H4 * 1kJ/ 1000j =12,420 KJ

12,420KJ * 1c/57Kj= 218C T f = 290K+218K=508K




Final P : PV=nRT ==> P=nRT/V

n=20 moles N2H4 react with 60 mole of O2 sp no left over O2


N2H4 + 3O2 ==> 2NO2 + 2H2O
20N2H4====> 40NO2 + 40 H2O =80moles

R= 0.0821L*atm /1mole *K

T=508K
V= 20L

P=nRT/V

= 80mol * 0.0821 L*at, / 1mol K * 508K * 1/20L = 167atm

 

[Amok]

You want to fine the final T for speeding :D ?

Anyway, what specifically don't you understand about this? And are you sure that Cp and not Cv is given?

 

[nevada2012]

ok i figure out the first step.
all that they did was converted from
moles to g to kg then multiply the specific heat then convert to J then to KJ then to C and then to K

now i am confuse as to how they found the P

i understand that the equation is pv=nrt which becomes p=nrt/v

but they did this

N= 20 moles N2H2 react with 60 mol O2 , so there is no left over O2
what i don't understand, is what do they mean by left over O2?

so then it continues with
N2H4 + 3O2 ==> 2NO2 + 2H2O

N2H4--->40NO2 + 40H2O = 80 moles

i don't understand how they got the second equation N2H4--->40NO2 + 40H2O = 80 moles


can't i just add 60 and 20 to get the 80moles?

thanks

 

[Amok]

The (properly equilibrated) chemical equation for the reaction gives you the proportions in which the reactants react with each other. In your case, for each mole of N2H4 you need 3 moles of O2 (thrice the amount of N2H4). That will give you 2 moles of NO2 (twice the amount of N2H4) and two moles of H20 (twice the amount of N2H4). If you have 20 moles of N2H4 you need 20*3 = 60 moles of O2, which is exactly what you have. Had you had 100 moles of O2, there would be 40 moles of O2 left over. Knowing that 20 moles of N2H4 will react, you know that you'll have 20*2 = 40 moles of each one of the products. Since 40 + 40 = 80, you'll end up with 80 moles of gas after the reaction finishes. Once again, had you had 100 moles of O2, you'd still have 80 moles of product by the end plus 40 moles of O2. In this reactions the total number of moles is conserved (1 + 3 = 2 +2 ), so it's easy. There are several reaction where moles of gas are created or destroyed. Most explosives, for example, involve reactions that produce huge amounts of gas, which will expand, creating massive destruction.

A chemical equation gives you the proportions of reactants you need and the proportion of the products you will obtain. That's what you need to keep in mind. You should always measure everything with respect to the quantity of limiting reactant (the reactant there's not enough of).

 

[LudusRex]

To find the final temperature (Tf), we first need to calculate the heat released in the reaction. We can do this by using the heat of combustion (Hc) of N2H4 and the number of moles of N2H4 present. We convert the moles of N2H4 to kilograms and then use the heat of combustion to calculate the heat released. Next, we use the heat capacity (Cp) of N2H4 to convert the heat released to a change in temperature. This gives us a change in temperature of 218K, which we add to the initial temperature (T1) of 290K to get the final temperature of 508K.

To find the final pressure (Pf), we use the ideal gas law, PV = nRT. We know the number of moles of N2H4 (20 moles) and the temperature (508K), and we can calculate the volume (V) using the given volume of 20L. This gives us a final pressure of 167 atm.

In summary, to find the final temperature and pressure, we used the heat released in the reaction and the ideal gas law, respectively. The steps involved converting units, using relevant constants, and applying the appropriate equations. I hope this explanation helps you understand how the final T and P were found.