# What is Partial pressure: Definition and 85 Discussions

In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas mixture is the sum of the partial pressures of the gases in the mixture (Dalton's Law).
The partial pressure of a gas is a measure of thermodynamic activity of the gas's molecules. Gases dissolve, diffuse, and react according to their partial pressures, and not according to their concentrations in gas mixtures or liquids. This general property of gases is also true in chemical reactions of gases in biology. For example, the necessary amount of oxygen for human respiration, and the amount that is toxic, is set by the partial pressure of oxygen alone. This is true across a very wide range of different concentrations of oxygen present in various inhaled breathing gases or dissolved in blood. The partial pressures of oxygen and carbon dioxide are important parameters in tests of arterial blood gases, but can also be measured in, for example, cerebrospinal fluid.

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1. ### Query re: Partial pressures of O2 in high vs low pressure environments

Hi, I'm currently learning to scuba dive and we use a very simple way to calculate the partial pressure of oxygen at depth to avoid oxygen toxicity, for example at sea level of 1 atm and 21% O2 concentration the partial pressure is calculated to be 0.21, and at 60m (pressure increases by 1 atm...
2. ### Calculating atmospheric partial pressure of oxygen

I study genotype-environment associations in alpine species. I frequently see altitude as the sole predictor of partial pressure of oxygen in the literature concerning hypoxia adaptations. However, I understand that partial pressure of oxygen is also influenced by temperature, humidity, and...
3. ### Finding partial pressure at equilibrium

In the coursebook the question says: The reaction below was carried out at a pressure of 10×10⁴ Pa and at constant temperature. N2 + O2 ⇌ 2NO the partial pressures of Nitrogen and Oxygen are both 4.85×10⁴ pa  Ccalculate the partial pressure of the nitrogen(ll) oxide, NO(g) at equilibrium. In...
4. ### About the binding of O2 to Hemoglobin molecules

Hello, I just learned about the binding capacity of Hemoglobin (Hb) and that it is proportional to the partial pressure of O2 in the blood here is the curve : it does have a sigmoidal shape, but here is the problem: in the lecture, it's said that Hb has an increasing affinity to O2 the more...
5. ### A question about chemical equilibrium

Hello we learned about the chemical equilibrium and how to write it's formula in the case of liquid and gaseous phase , what about a reaction involving different phases ? like this one : how do we write the formula for the chemical equilibrium ? do we just ignore the carbon ,is there any rules...

7. ### Chemistry Partial pressure of He in this gas mixture

My progress: P(HE) = 0.877*0.75/(0.75+0.5) = 0.5262 atm is this right?
8. ### Partial pressure of oxygen at a certain altitude

The pressure of oxygen at sea level = ##\frac{20.9}{100} ~\text{x} ~(21.2 ~\text{x} ~ 10^3) = 4430.8~ \text{Pa}## Then I do not know how to calculate the pressure at altitude 7000 m. I tried using P = ρgh (taking ρ as density of air = 1.3 kg/m3) then subtract the result from 4430.8 Pa but got...
9. ### Chemistry What are the partial pressures of each gas in the mixture?

I've first calculated the partial pressures of each gas: ##N_2: 0.4\times 7.4\times 10^4=3.0\times 10^4 Nm^{-2}\\## ##O_2: 0.35\times 7.4\times 10^4=2.6\times 10^4 Nm^{-2}\\## ##CO_2: 0.25\times 7.4\times 10^4=1.9\times 10^4 Nm^{-2}\\## From here, I do not know how to continue. Could someone...
10. ### Chemistry Equilibrium Partial Pressures

Homework Statement Kc = 4.15 x 10-2 at 356°C for PCl5(g) ↔ PCl3(g) + Cl2(g). A closed 2.00 L vessel initially contians 0.100 mol PCl5. Calculate the total pressure in the vessel (in atm to 2 decimal places) at 356°C when equilibrium is achieved. Homework Equations PV=nRT Kp= Kc(RT)^change in...
11. ### Difference between Oxygen Tension and Partial Pressure

Homework Statement What's the difference between Oxygen Tension And Partial Pressure Homework Equations ...uh...rules of grammar ? The Attempt at a Solution If I knew the solution I wouldn't be here now would I ? Here are a few links https://en.m.wikipedia.org/wiki/Blood_gas_tension...
12. ### Why does the partial pressure of H2O stay the same

https://ibb.co/dxwnMe https://ibb.co/miNu1e In these slides they show the partial pressure of the H2O gas not changing when the enternal pressure on the entire gas is increased. Why is this the case? I know it condenses to maintain the same partial pressure, but couldn't the partial pressure of...
13. ### Various Pressures in mass transfer

I'm confused between partial pressure, total pressure, boiling point , vapour pressure , saturation pressure and saturation temperature.These things haunt me in my subject mass transfer. I get really confused when this words come in a liquid - vapour system, I cannot identify what these pressure...
14. ### Dalton's law of partial pressure

Does anyone know a rigorous proof for Dalton's law ? I think I saw it once, but I can not find it again anywhere. Thanks Ric
15. ### Themodynamics: calculating the partial pressure with Dalton's Law

Homework Statement In a sealed container is Helium ##M_{He} = \frac {4kg} {kmol} ## with a pressure of ## p_{He} = 4bar##. now is Methan put isothermic inside the container till both the methan and the helium mass are equal( ##M_{CH4} = \frac {16kg} {kmol} ## Calculate using the ideal gas law...
16. ### Difference between Partial pressure and vapor pressure

Partial pressure must be less than or equal to the vapor pressure if there is no liquid present. However, when both vapor and liquid are present and the system is in the phase equilibrium, the partial pressure of the vapor must be equal to the vapor pressure and system is said to be saturated...
17. ### Partial pressure problem?

A sample of argon gas is collected over water at 30.0oC. The level of the water is adjusted until the total pressure in the flask is 771 torr and the volume is 250.0 mL. The vapor pressure of water is 31.8 torr at 30.0oC. A. How many moles of argon are in the flask? B. What is the partial...
18. ### What equivalence of vacuum in pressured system is possible?

If I have a volume of gas in a sealed container with a special one way valve in it, and I heat the gas inside the container, the pressure increases and some gas escapes through the valve to the outside. I now have less atoms of gas inside the container, which, when cooled back to the starting...
19. ### Calculating the total and partial pressure of gas mixture

1. The problem/question is as follows: 1 mole of O2 mixed with N2 gas (PN2= 5 atm at 10 degrees celcius in a 1 L flask. What is the total pressure after 2 moles of gas is allowed to escape? How about the partial pressure of O2? R= 0.08206\frac{L atm}{mol K} Homework Equations Using the ideal...
20. ### Partial Pressure of a Vapour

1) We know that when both liquid and vapor are present, and system of these is in phase equilibrium; the "partial pressure of the vapor" must be equal to the "vapor pressure" , i.e. : partial pressure of vapor= vapor pressure. 2) However, what happens if there is no liquid in the system, i.e...
21. ### Pressure inside a heated sealed vessel

Please can you help me de find out the calculation steps leading to the partial pressure inside a heated closed vessel with 25 ml total capacity but filled 20mL with aquous mixture of 2 acids(HNO3/HF ;1/3)..I think to simplify the problem we could at a fisrt approximation assume that the mixture...
22. ### Why are the conditions of ΔG° partial pressure fixed at 1bar

Shouldn't the ΔG° partial pressure of the components be based on the K? Where ΔG°=-RTlnK such that K is based on the partial pressures of the gas involved? If we were to set the partial pressure to be 1bar each then every reaction having the same stoichiometric proportion of reactants and...
23. ### Finding partial pressure with only T, V and ambient P

Homework Statement 60 L of N2 are collected over H2O at 40oC when atmospheric pressure is 760.00 torr. What is partial pressure of N2? Homework Equations PV=nRT Pt=P1+P2... Vapor pressure of H2O at 40oC:7.3590 KPa 760 torr=101.3 kPa 40oC=313oK The Attempt at a Solution PV-nRT...
24. ### Chemistry Partial pressure vs mole fraction graph

Homework Statement There is a statement in a book : " Graph of P vs ##\chi## is a straight line which ##cannot## pass through origin" Homework EquationsThe Attempt at a Solution But if mole fraction of a component is zero then it can't form vapours because of which its partial pressure will be...
25. ### Equilibrium of ammonia synthesis

Homework Statement In order to obtain commercial conversion levels in the production of ammonia, reactors operate between a pressure range from 150 to 300 atm, and a temperature range from 700 to 750 K. Calculate the mole fraction of N2 when the reaction reaches equilibrium at 300 atm and 723...
26. ### Psychrometry -- Ethanol in dry air

Homework Statement Ethanol evaporates in a 10 x 20 x 50 ft3 room. Air is initially dry at a temperature of 30 °C and 765 mmHg of pressure. a) If the partial pressure of ethanol after vaporization is 40 mmHg, how many pounds of ethanol evaporated? b) The same air is compressed until it reaches a...
27. ### Rate constant and partial pressure

Homework Statement The rate constant for the conversion of methyl isonitrile is 5 x 10^-5. A scientist has a container containing this substance with a partial pressure of 100 torr. After 12.8 hours (46,000 seconds), what is the partial pressure of methyl isonitrile gas inside the container...
28. ### Partial pressure of water vapor

Homework Statement The partial pressure of water vapor in air at 200 is 10[mm] mercury. according to the table of partial pressures we have to cool the air to 11.40 in order to bring the air to saturation, that is100% relative humidity. this according to the book. But when we cool the pressure...
29. ### Solubility in Relation to Partial Pressure vs. System Pressure

Hi Physics Forums, The solubility of a gas according to Henry's Law depends on partial pressure. Would an increase in pressure in a system increase the solubility of a specific gas, even if the partial pressure of that particular gas doesn't change? The system described above increases in...
30. ### Ideal Gas Law solve for partial pressure

1. Gaseous compound Q contains only xenon and oxygen. When 0.100 g of Q is placed in a 50.0 mL steel vessel at 0 °C, the pressure is 0.229 atm. When the vessel and its contents are warmed to 100 °C, Q decomposes into its constituent elements. What is the total pressure, and what are the partial...
31. ### Partial Pressure at equilibrium

Homework Statement H2(g) + S(s) = H2S(g) Kc= 6.8x10^-2 If 0.2 moles of H2 and 1.0 mole of S are heated in a 1L vessel upto 90C, what will be the partial pressure of H2S at equilibrium? Can someone help me with this step by step?Homework Equations The Attempt at a Solution Kc = 6.8X10^-2 = x /...
32. ### Partial pressure ratio of gases at different altitudes

Homework Statement On a planet not entirely unlike earth, the ratio of the partial pressure of N2 to that of O2 equals 1 at an altitude of 1 km: \frac{p_{\text{N}_2}}{p_{\text{O}_2}} = 1. Assuming that T = 200 K, and the gravitational constant is 5 m/s2, what is the ratio...
33. ### Partial Pressure Equilibrium

Homework Statement Ammonia gas decomposes to nitrogen and hydrogen spontaneously with an equilibrium constant, Kp = 5.9 x 109. Calculate the partial pressure of ammonia at equilibrium given that the partial pressure of nitrogen and hydrogen are both 2.7 atm initially. [Hint: If you need...
34. ### Partial Pressure Question

Hello, first post here. Here is a hypothetical partial pressure of gas question Imagine you have a two component system: Component 1 is water Component 2 is an imaginary substance that is immiscible with water, but has same boiling temp / pressure You put the two components in a...
35. ### Partial Pressure of He, Ne, Ar in 0.80 atm Mixture

Homework Statement A mixture of He, Ne, and Ar has a total pressure of 0.80 atm and is found to contain 0.55 mol He, 0.94 mol Ne, and 0.35 mol Ar. What is the partial pressure of each gas in atm? Homework Equations Partial pressure for a gas is equal to the mole fraction of the gas...
36. ### Partial Pressure of a Hg-N2 System

Homework Statement At 1 atm of pressure a volume of 22 liters of N2 gas is passed in a closed system over a boat containing Hg liquid at 100°C. The flow of N2 is slow to allow the gas to become saturated with mercury. At 20°C and 1 atm, the nitrogen was found to contain 0.0647g of Hg...
37. ### Partial Pressure Calculation

Homework Statement I am given the following equation: 2NO (g) + Cl2 (g) \rightleftharpoons 2NOCl (g) Kp = 6.5×104 PNO = 0.35 atm PCl2 = 0.10 atm I need to calculate PNOCl. Homework Equations Kp = \frac{(P_{NOCl})^2}{(P_{NO})^2*(P_{Cl_2})} The Attempt at a Solution I...
38. ### What is the partial pressure of co2(product) given the v,t of 2 reacta

Homework Statement Hi In a container of 1.5L there are 2 gases O2 and C3H8. their partial pressures are O2 = 5atm, C3H8=0.1atm. the temperature is 20C. the reaction produces H2O and CO2. Temperature is constant. What is the partial pressure of CO2 after the reaction? (need to find...
39. ### Partial Pressure: Higher SP Determines P

Am I assuming right the pressure in a vessel holding two substances (both being in the both liquid and gas states) will be equal to the saturation prerssure of the one which has the higher SP ? That is, for substance A whose SP at a given temp. is 10 B, for instance, and substance B whose SP is...
40. ### What is the Kp of H2 and CO in a Partial Pressure Problem?

Homework Statement when steam was heated with excess carbon in a closed container to 1800kpa, the partial pressure of steam at equilibrium of steam was 318kpa, find Kp H2 ,Kp CO and find Kp Homework Equations H2O(g) + C(s) -> H2(g) + CO(g) <-...
41. ### Equilibrium Partial Pressure Kp/Kc Question

Homework Statement At 100 o C Kc=.078 for the reaction SO2Cl2<-->SO2 + Cl2. In an equilibrium mixture the [SO2CL2]=.0108 M and [SO2]=.052 M. What is the partial pressure of Cl2 in the eq. mixture? Homework Equations Kp=Kc(RT)\Deltan P=RT/V The Attempt at a Solution I solve for...
42. ### Measurning the partial pressure of a component of a solution in equilibrium

Homework Statement Suppose I have two substances in a solution, each forming an equilibrium with its corresponding vapor phase, and thus having its own partial pressure. How can I measure this partial pressure of one of the components, given the pressure of each component in its pure form...
43. ### Partial Pressure Quest: 2L Vessel, PCl5 Decomposition @ 250C

We have an empty vessel with volume of 2L. We put 2.42gr of PCl5 (g) and allowed it to partially decompose at 250 Celsius according to: PCl5 --> PCl3 + Cl2 the two prodcuts are also gases. The total pressure inside the vessel after this partial decomposment is 359 torr. What is the partial...
44. ### Determine the partial pressure of gas at equilibrium

I figured out the answer to this already, but I wanted help on the reasoning behind it: In order to work out the problem we're supposed to determine the partial pressure of phosgene by subtracting 0.497 atm worth from the initial pressure of 1.31 atm (determined by using the ideal gas...
45. ### Partial Pressure Help-Please Check

Partial Pressure Help---Please Check The Partial Pressure of water vapor at T = 273 K is 6.11 mbar. Find the corresponding mass concentration of water vapor. Assume P = 1 atm. So... ρH20 = (PH20*MH20/(R*T) ρH20= (6.11*10^2 Pa)*(18.01 g/mol)/(8.314*273 K) ρH20 = 11004.11/2269.722 =...
46. ### How much gas is released given partial pressure

Homework Statement The solubility of N2 in blood at 37 degree and at a partial pressure of 0.8 atm is 5.6 x 10-4 mol/L? a deep sea diver breathes compressed air with the partial pressure of N2 equal to 4 atm. Assume that the total volume of blood in the body is 5 L. Calculate the amount of N2...
47. ### What are the partial pressures of H2, Br2, and HBr at equilibrium?

Homework Statement at 1000K, Kp=1.2*10^6 and Delta H = -101.7 kJ for the reaction H2(g)+ Br2(g) <-->2HBr. A 0.952 mol quantity of Br2 is added to a 1.00L reaction vessel that contains 1.25 mol of H2 gas at 1000K . What are the partial pressures of H2 ,Br2 ,HBr and at equilibrium?Homework...
48. ### Chemistry Partial pressure and moles problem?

Homework Statement Here is the problem: Carbon monoxide and oxygen are kept at exactly 300 K in separate chambers of the apparatus shown below. When the stopcock is opened, the combustion reaction begins and is allowed to proceed to completion, while being maintained at exactly 300 K...
49. ### Calculating the partial pressure of pure Zinc over a solution? over

Homework Statement The activity coefficient of zinc in liquid brass is given (in joules) by the following equation for temperatures 1000-1500 K: RT ln γZn = -38,300 x2Cu where xCu is the mole fraction of copper. Calculate the partial pressure of pure zinc PZn over a solution of 60 mol%...
50. ### Carbon dioxide partial pressure

Homework Statement Carbon dioxide partial pressure: a. increases in the blood as it travels from the systemic venules to the inferior vena cava b. is greater in the blood in the systemic capillary beds than in the alveoli of the lungs. The Attempt at a Solution The answer is...