# Enthelpy change of reaction

• Chemistry
• Tasha Clifford
In summary, the conversation discusses the relationship between pressure and enthalpy of ideal gases, as well as the use of Hess' law to calculate enthalpy at different temperatures. The participants also touch on the concept of ideal gases and how they are used in thermodynamic reactions. The conversation ends with doubts about the understanding of the topic and the need for a textbook.

#### Tasha Clifford

Homework Statement
What can be done to increase the enthalpy of the following system and how this happen?

A.By increasing the pressure of the
system
B.By decreasing the pressure of the system
C.By increasing the temperature
D.By decreasing the temperature
E .no n e o f t h e ab o v e
Relevant Equations
N2O4(g)+Heat⇌2NO2(g)
∆Hrxn = +ve at constant temperature
I feel that the answer is B)
because Increasing the pressure increases the intermolecular forces Of the gas molecules but I do not see how this In effect will lead to an increase in the enthalpy

You’re on the wrong track. If they are ideal gases, do their enthalpies depend on pressure? Are you familiar with Hess’ law?

Chestermiller said:
You’re on the wrong track. If they are ideal gases, do their enthalpies depend on pressure? Are you familiar with Hess’ law?
Yes Hess’s law states that the heat change in a chemical reaction is the same regardless of the number of stages taken to obtain the final product

But how does it relate to this qeustion

Tasha Clifford said:
Yes Hess’s law states that the heat change in a chemical reaction is the same regardless of the number of stages taken to obtain the final product

But how does it relate to this qeustion
You didn't answer my question about the effect of pressure on enthalpy of an ideal gas.
With regard to Hess' law, suppose you knew the change in enthalpy for a reaction at one temperature and you wanted the change in enthalpy at a higher temperature or lower temperature. How would you use Hess' law to find it?

Chestermiller said:
You didn't answer my question about the effect of pressure on enthalpy of an ideal gas.
With regard to Hess' law, suppose you knew the change in enthalpy for a reaction at one temperature and you wanted the change in enthalpy at a higher temperature or lower temperature. How would you use Hess' law to find it?
To be honest with you sir I haven’t an idea

I was just doing some research now and I found out that the enthalpy of ideal gases strictly depends on temperature and that there will be no change in enthalpy for an isothermal reaction involving ideal gases

Does this mean the answer is none of the above

I would also love to know How i could use Hess' law to find the new enthalpy as you say

Another question i have is how do i know that the Gases involved are ideal gases

or is that all gases involved in Thermodynamic reactions are generally considered ideal

Tasha Clifford said:
To be honest with you sir I haven’t an idea

I was just doing some research now and I found out that ...there will be no change in enthalpy for an isothermal reaction involving ideal gases.
This is incorrect. There is definitely a change in enthalpy for an isothermal reaction involving ideal gases. You seems to be "in over your head" with this. Are you studying thermo on you own?

Tasha Clifford said:
Does this mean the answer is none of the above
No. Also, it seems like something is omitted from the problem statement. What is the exact wording of the question
Tasha Clifford said:
I would also love to know How i could use Hess' law to find the new enthalpy as you say
Do you have a textbook?
Tasha Clifford said:
Another question i have is how do i know that the Gases involved are ideal gases

or is that all gases involved in Thermodynamic reactions are generally considered ideal
The gases involved are not necessarily ideal, but the pressure effect is a little advanced for your apparent level of progress. Anyway, if you can't answer this for ideal gases, you certainly won't be able to for real gases.