How can I apply Hess's Law to solve a thermodynamics homework problem?

In summary, to solve this problem, you must first balance the given equations and then work backwards to manipulate the reactions and their respective enthalpy values to obtain the desired reaction: N2O (g) + NO2(g) --> 3NO (g). This can be done systematically by identifying and manipulating equations that contain the desired reactants and products.
  • #1
courtrigrad
1,236
2
Hello all

Given

(a) N2(g) + O2(g) --> 2NO(g) ∆H = + 180. 7 kJ

(b) 2NO(g) +O2(g) --> 2NO2(g) ∆H = -113.1 kJ

(c) 2N20(g) --> 2N2(g) --> O2(g) ∆H = -163.2 kJ

Desired Reaction: N2O (g) + NO2(g) --> 3NO (g)

Can someone please tell me where to start? How do I apply Hess's Law? I know I have to work backwards. However, how do I do this in a systematic way?

Any help is appreciated

Thanks
 
Last edited:
Physics news on Phys.org
  • #2
courtrigrad said:
Hello all

Given

(a) N2(g) + O2(g) --> 2NO(g) ∆H = + 180. 7 kJ

(b) 2N)(g) +O2(g) --> 2NO2(g) ∆H = -113.1 kJ

(c) 2NO2(g) --> 2N2(g) --> O2(g) ∆H = -163.2 kJ

Desired Reaction: N2O (g) + NO2(g) --> 3NO (g)

Can someone please tell me where to start? How do I apply Hess's Law? I know I have to work backwards. However, how do I do this in a systematic way?

Any help is appreciated

Thanks

please rewrite the equations. Just look at B), for instance, it's not even balanced... and C makes no sense since how can you get O2 from 2 N2...
 
  • #3
A good place would be to state the equations correctly:
[tex] N_{2}+O_{2}\rightarrow 2NO [/tex] [tex] (\Delta H)_{1}=+180.7 kJ [/tex]

[tex] 2NO+O_{2}\rightarrow 2NO_{2} [/tex] [tex] (\Delta H)_{2}=-113.1 kJ[/tex]

[tex] 2NO_{2}\rightarrow N_{2}+2O_{2} [/tex] [tex] (\Delta H)_{3}=-67.6 kJ [/tex]

Now,which is the quantity u want to compute and what's the reaction u wish to get??

Daniel.
 
  • #4
I want to compute ∆H for

N2O (g) + NO2(g) --> 3NO (g)
 
  • #5
I think C should be 2 N2O(g) -> 2N2(g) + O2(g)...

Balance the reactions so that you will get rid of the unwanted reactants or products... For instance, N2 + O2 -> 2NO

you you might want to multiply the reaction by 2 since N2 is not wanted and there's an N2 in reaction C of the product. I am assuming you know they will cancel out when added together...
 
Last edited:
  • #6
yes but is there an actual method to solve the problem? Or do you have to just guess and check?
 

1. What is thermodynamics?

Thermodynamics is the study of how energy is transferred between different forms and how it affects matter. It also deals with the properties of materials and how they change in response to energy.

2. Why is thermodynamics important?

Thermodynamics is important because it helps us understand and predict the behavior of matter and energy in various systems. It also has many practical applications, such as in the design of engines, refrigerators, and power plants.

3. What are the laws of thermodynamics?

The laws of thermodynamics are fundamental principles that govern the behavior of energy in a system. The first law states that energy cannot be created or destroyed, only transferred or converted. The second law states that the total entropy, or disorder, of a closed system will always increase over time. The third law states that the entropy of a perfect crystal at absolute zero temperature is zero.

4. How do you solve thermodynamics problems?

To solve thermodynamics problems, you need to identify the system and its surroundings, determine the type of energy transfer involved (heat or work), and apply the appropriate equations and laws. It is also important to carefully define variables and units, and to check for any assumptions or simplifications made.

5. What are some real-life applications of thermodynamics?

Thermodynamics has many practical applications in our daily lives. Some examples include the operation of car engines, refrigerators and air conditioners, power generation in power plants, and the behavior of chemical reactions. It is also used in the study of weather patterns, climate change, and the formation of stars and galaxies.

Similar threads

  • Introductory Physics Homework Help
Replies
29
Views
3K
  • Introductory Physics Homework Help
2
Replies
41
Views
2K
  • Biology and Chemistry Homework Help
Replies
17
Views
2K
  • Introductory Physics Homework Help
2
Replies
37
Views
3K
  • Introductory Physics Homework Help
Replies
24
Views
2K
  • Biology and Chemistry Homework Help
Replies
4
Views
2K
  • Introductory Physics Homework Help
Replies
5
Views
2K
  • Biology and Chemistry Homework Help
Replies
1
Views
4K
  • Biology and Chemistry Homework Help
Replies
3
Views
2K
  • Biology and Chemistry Homework Help
Replies
1
Views
2K
Back
Top