# Vapor pressure vs liquid pressure in enthelpic combustion reaction

• enantiomer
In summary, the given combustion reaction will produce liquid water instead of water vapor, due to the equilibrium vapor pressure of water being lower than the partial pressure of water vapor in the reaction. This can be determined using the enthalpy of formation, partial pressures, and the ideal gas law. The stoichiometry of the reaction also needs to be considered in order to accurately determine the partial pressure of water vapor.
enantiomer

## Homework Statement

Hi guys,
I'm a little lost on what should probably be a simple question
Using the following combustion reaction
(C7O2H6)s + 7.5 (O2)g --> 7 (CO2)g + 3 (H2O)l
the equation indicates that water produed by the reaction is liquid water not water vapor. Is this correct? Explain. The equilibrium vapor pressure of water is 22.38 torr at 24 C and 25.21 at 26 C.

## Homework Equations

I think they're asking us to use ΔfH(l)[/SUP€]*Pp(l) + ΔfHg*Pp (g)
where Pp is the partial pressure of H2O as either a gas or a liquid and H is the enthalpy of formation of the either the liquid or the solid.
However now I'm stuck because I don't know how to get the partial pressures for the equation,
If I'm right with this equation can someone let me know what I'm missing?
If I'm wrong can someone tell me where I messed up?

Side note: I went to the TA and he mentioned that weighted averages should help with the reaction, but I'm still confused?

Hello,

You are on the right track with using the enthalpy of formation and partial pressures to determine the state of water in this reaction. However, there are a few things you are missing.

Firstly, the equilibrium vapor pressure of water is important to consider in this reaction. Since the reaction is taking place at a temperature between 24 C and 26 C, we can assume that the partial pressure of water vapor will be between 22.38 torr and 25.21 torr. This means that the partial pressure of water vapor in the reaction will be less than the equilibrium vapor pressure, and therefore, the water produced will be in liquid form.

Secondly, you need to consider the stoichiometry of the reaction. The given equation shows that for every 7.5 moles of oxygen gas, 3 moles of water are produced. This means that the partial pressure of water vapor will be 3/7.5 times the partial pressure of oxygen gas.

Finally, to determine the partial pressure of water vapor, you can use the ideal gas law: PV = nRT. Since you know the temperature and the partial pressure of oxygen gas, you can solve for the partial pressure of water vapor.

I hope this helps. Let me know if you have any further questions. Good luck with your work!

## 1. What is the difference between vapor pressure and liquid pressure in enthalpic combustion reactions?

The vapor pressure of a substance is the pressure at which its gas and liquid phases are in equilibrium. In enthalpic combustion reactions, the vapor pressure refers to the pressure exerted by the gaseous products of the reaction. On the other hand, liquid pressure refers to the pressure exerted by the liquid reactants in the reaction.

## 2. How does vapor pressure affect the rate of enthalpic combustion reactions?

The vapor pressure of a substance is directly related to its concentration in the gas phase. Higher vapor pressure means a higher concentration of the gaseous products, which can increase the reaction rate. This is because more collisions between reactant molecules occur, leading to a faster reaction.

## 3. Can vapor pressure and liquid pressure be manipulated to control enthalpic combustion reactions?

Yes, vapor pressure and liquid pressure can be manipulated by changing the temperature or pressure of the reaction environment. This can alter the equilibrium between the gas and liquid phases, affecting the concentration of reactants and products and ultimately controlling the reaction rate.

## 4. How does enthalpy change in enthalpic combustion reactions?

In enthalpic combustion reactions, the enthalpy change refers to the difference in energy between the reactants and products. This energy is usually released in the form of heat. The enthalpy change is typically negative, indicating an exothermic reaction where energy is released.

## 5. What factors can affect the vapor pressure and liquid pressure in enthalpic combustion reactions?

The vapor pressure and liquid pressure in enthalpic combustion reactions can be affected by factors such as temperature, pressure, and the nature of the reactants and products. Additionally, the presence of catalysts or inhibitors can also influence the pressure of the system and therefore impact the reaction rate.

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