Questions tagged [pressure]
For questions about gas pressure, or the effect of pressure in general on chemical species, substances, or reactions.
309 questions
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Relationship between the partial pressure $p_J = x_J p$ and the perfect gas law $pV = nRT$
I am currently studying Atkins' Physical Chemistry, 11th edition, by Peter Atkins, Julio de Paula, and James Keeler. Chapter 1A.2 Equations of state says the following:
When dealing with gaseous ...
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Pressure exerted by a particle of ideal gas
There is a step I fail to grasp in the proof that for a monatomic ideal gas, $U=\frac{3}{2}PV$, where $U$ denotes the internal energy of the gas.
The proof involves considering a particle with mass $m$...
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How does pressure influence the dehydration of salts?
It's well known that the boiling point of a substance increases with pressure. I was wondering if something similar happens with hydrated salts and the temperature at which they dehydrate.
I mean, if ...
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Can Gay-Lussac's law be observed in the reverse direction?
Gay-Lussac's law states that if you decrease the temperature of a gas at constant volume, the pressure decreases by a corresponding amount. This is easy to carry out experimentally. But in practice is ...
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Latent Heat, Vapor pressure and Equilibrium [duplicate]
So after reading about this topic i wanted to share what i learned and i wanted you guys to tell me if what i am writting is correct:
A pressure vessel has propane inside and it is pressurized. The ...
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Measuring vapour pressure in a closed system
My experiment requires the determination of vapour pressure from which I will calculate the number density (or number of moles of the molecule) later, for a closed system.
Here's my setup :
Liquid ...
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What is the effect of pressure upon the melting and boiling points of a substance? [closed]
I want to know about the inter-relation between the effect of pressure upon the melting and boiling points of a substance. Can anyone help?
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Shouldn't the pressure of gas above a liquid slightly decrease when some of its molecules dissolves in the liquid? [closed]
Lets say a liquid and gas above are in equilibrium.
(1) Now if I suddenly increase the pressure of the gas it will take some time for some molecules of the gas to enter the liquid and get dissolved. ...
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Doubt about definition of boiling point [duplicate]
The definition of boiling point says boiling point is the temperature at which the vapour pressure of liquid becomes equal to vapour pressure of atmosphere. But how does the vapour pressure of the ...
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Why are pressure or volume not able to change the equilibrium constant? [duplicate]
It is stated in my textbook that temperature is the only factor that can change the equilibrium constant. According to the Ideal Gas Law, temperature is dependent on the pressure and volume. Thus, ...
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Clausius–Clapeyron equation: shape of phase diagrams makes no sense
I am trying to model the melting point of a substance at varying pressures (ranging from very small to very very large). All I am trying to do is make an equation that relates melting temperature to ...
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Percent degree of dissociation of gas by pressure
I stumbled across the following interesting problem:
Assume that you have started to live on a new planet where standard pressure condition is $\pu{2 bar}$, standard concentration is $\pu{1 M},$ and ...
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What is the vapor pressure of a liquid if it is not in a sealed container(i.e., a river or lake)? Is it just the atmospheric pressure? [closed]
From what I understand, the boiling point of a liquid is when its surrounding pressure is equal to its vapor pressure. The vapor pressure is the pressure of the gas form of the liquid in a container ...
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Why is gas pressure measured in mmHg?
Pressure can be measured in $\pu{mmHg}$ which is equal to the pressure exerted by a “column of mercury” of a height expressed in $\pu{mm},$ at $\pu{0 °C}$ under Earth’s normal gravity.
Does the ...
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What actually happens to the volume of a gas in an isolated system?
In an isolated system with adiabatic walls in which gas is filled what exactly happens? How do we define the volume of a gas here? Is volume of 1 mole of gas present in that inelastic container the ...
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What's the effect of Pressure change in Chemical Equilibrium if any reactant or product is Solid or Liquid?
I am studying Le Chatelier's Principle of Chemical Equilibrium. I am trying to solve a problem involving the effect of a pressure change on a chemical equilibrium.
I know that if a reversible reaction ...
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How do you manage to liquefy a gas by applying only pressure? [closed]
How can you liquefy a gas by applying only pressure? To increase the pressure of a gas you need a compressor, and when the compressor does work on the gas , it will increase his pressure but at the ...
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Equilibrium: Effect of change in composition and value of Kp, Kc on changing pressure
Di-hydrogen gas is obtained from natural gas by partial oxidation with steam as per following endothermic reaction:
$CH_4{_{(g)}}+H_2O_{(g)} \ce{<=>} CO_{(g)}+3H_2{_{(g)}}$
How will ...
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Decarboxylation of THCA during CO2 Extraction of Cannabis
We have a strange problem. We are performing CO2 extraction on cannabis and we are seeing considerable decarboxylation of THCA to THC.
We have high quality temperature sensors at the heat exchangers, ...
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Determining molar mass of protein from osmotic pressure
A 299 mL solution containing 21 g of a protein in toluene had an osmotic pressure of 0.053 atm at 27 degrees Celsius. What is the molar mass (in g/mol) of the protein?
We can use the formula that
$$\...
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Using osmotic pressure to find the molar mass of a compound
Working on-board a research vessel somewhere at sea, you have (carefully) isolated 12.5 micrograms $(\pu{12.5E-6 g})$ of what you hope is pure saxitoxin (a non-electrolyte) from a poisonous (and quite ...
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membrane for a reverse osmosis desalination experiment
We are second year cram schoolers , we are currently working on a project tackling water desalination by reverse osmosis and are required to do an experience. During the process, we encountered some ...
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how to Find $P_{tot}$ Given that $K_p = 28.5$ and the partial pressure at equilibrium
I have the equilibrium equation :
$4KO_2{_{(s)}} + 2CO_2{_{(g)}} \ce{<=>} 2K_2CO_3{_{(s)}} + 3O_2{_{(g)}}~~k_p = 28.5 ~at ~25C$.
Given that The partial Pressure of $CO_2$ is $0.191~atm$ at ...
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Finding the partial pressure
So I saw this problem but can't seem to figure out how to get the answer. I got a test tomorrow lol.
41) $\ce{SO2Cl2}$ decomposes in the gas phase by the following reaction:
$$\ce{SO2Cl2 -> SO2(g)...
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Impregnating polyethylene with oil using pressure cooker?
I have some polyethylene spiral wrap that I'm hoping to impregnate with citrus oil as an animal deterrent.
Wikipedia says that polyethylene plastic will pass through "flavourings" fairly easily. It's ...
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What is the triple point pressure for Gallium?
I have seen various discussions about the triple point of Gallium determined to a very precise value, so precise that it is used as a reference for NIST scales and measurements.
However, these ...
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Regarding units of water potential and chemical potential
If water potential is nothing but the chemical potential of a given solution, then why do their units differ?
If the unit for the latter is taken as 'Energy per molecule' (which makes sense to me ...
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How to find the final pressure excerted by a mixture of gasses which are then released from a vessel after succesive fillings?
The problem is as follows:
$5\ \mathrm l$ of oxygen at $2\ \mathrm{atm}$ of pressure and $10\ \mathrm l$ of nitrogen at $4\ \mathrm{atm}$ are collected in a vessel of $2\ \mathrm l$ in capacity. ...
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Why is so different the temperatures of a compressed gas compared to a liquid/gas mixture of the same fluid and they are both at the same pressure?
Why does $\ce{C3H6}$ gas when compressed (in a centrifugal compressor) comes out with a pressure of $\pu{16 bar}$ and $\pu{90 °C},$ and when it is a mixture of $\ce{C3H6}$ liquid/gas stored inside of ...
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Pressure vs volume plot for real gas and ideal gas
Background
Recently I have been studying about the states of matter and came to the topic of ideal gases and real gases, and the laws related to them. While studying it from my textbook, I saw the ...
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Is the heat for constant pressure the same as for constant volume in the formation of nitric oxide?
In the reaction $\ce{N2 (g) + O2(g) -> 2NO (g)}$
my textbook[1] says $q_v$ and $q_p$ are not the same, without any explanation.
I know that
\begin{align}
\Delta U &= q_p + w\\
\Delta U &=...
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About the use of pascal or atmosphere in chemistry
I was wondering if there are specific formulae in chemistry for which it is "compulsory" or convenient to use atmosphere (atm) rather than pascal (or even mmHg) as a unit of measurement.
Of course, ...
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What exactly causes equilibrium to shift when pressure is decreased? [duplicate]
Take the reaction:
$$\ce{N2(g) + 3 H2(g) <=> 2 NH3(g)}$$
If pressure is decreased, equilibrium shifts to the left because it has more moles. I understand the basics of why this is, i.e. due to ...
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Using Le Chatelier's Principle to Change Mechanical Energy to Chemical Energy
I was interested in an application of Le Chatelier's principle, where an increase in pressure could result in a decrease in the moles of gas.
In particular, a situation where when the pressure ...
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Calculating partial pressure of carbon monoxide
$\ce{ZnO}$ is exposed to pure $\ce{CO}$ at $\pu{1300 K}$ and the equilibrium
$$\ce{ZnO(s) + CO(g) <=> Zn(g) + CO2(g)}$$
is then established at $\pu{1 atm}$ pressure. The density of the gas ...
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Vapor pressure vs. ambient pressure
I've managed to get myself thoroughly confused in thinking about the vapor pressure of a substance at a particular temperature $T$, and how it relates to the pressure of the substance if it is in a ...
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Why does reducing the pressure in an equilibrium reaction favour the side with more moles of gas?
I was trying to explain it in terms of reaction rates and such; more than just 'Le Chatelier's principle states ...', but I can't figure out the underlying reason as to why. I can explain why for ...
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Isothermal vs adiabatic compression of an ideal gas [closed]
Could someone please explain these specific questions physically (especially the first question!)? I understand the corresponding mathematical proofs, but not the physical reasoning? I have looked ...
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Which pressure is used for calculation of standard enthalpy change of the reaction with two or more gases?
Standard state conditions for standard Gibbs free energy change stipulate (among other conditions) that the partial pressure of each gas is $\pu{1 bar},$ e.g. for the reaction
$$\ce{2 A(g) + 3 B(g) &...
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How to derive this temperature-pressure-specific volume relationship?
(for isentropic, adiabatic, ideal gas flow)
$$\frac{T_x}{T_y} = \left(\frac{p_x}{p_y}\right)^{\frac{(\gamma-1)}{\gamma}} = \left(\frac{V_y}{V_x}\right)^{\gamma-1}$$ where $V$ is the specific volume, $...
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Coffee cup lids
So this morning I purchased a coffee. As a not uncommon event the lid on the coffee cup didn't have a hole completely punched through (a gas inflow hole). This makes it difficult to drink the coffee ...
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Stritations in a discharge tube
I am reading about A cathode ray discharge tube and I still do not fully understand why that as you keep on lowering the pressure in the chamber it creates striations, Faraday's dark space and Crooke'...
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Proper (and safe) way to pressurize a vessel to around 70 kPa with gentle (~38* C) heat [closed]
I'm trying to force crystallization in a complex mixture by maintaining gentle pressure and heat. I'm thinking of using a Duran pressure plus bottle with a cap that has 2 GL-14 fittings, one attached ...
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How to calculate the aqueous solubility of CO2 vs Pressure
I would like to make Na2CO3 react with HCl in a closed fixed volume vessel, and accordingly I'd like to understand how ensuing pressure will affect the equilibrium of my reaction (and to which extent ...
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Calculating partial pressure equilibrium constant Kₚ given initial pressure and equilibrium pressure
A reaction
$$\ce{A(g) <=> B(g) + C(g)}$$
happens in constant volume and constant temperature. The reaction starts only with gas $\ce{A}$ (no $\ce{B}$ or $\ce{C}$) with given pressure $P_1 = \pu{...
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Metering Device decreases pressure yet produces saturated liquid?
This question pertains to the change of state of liquid using a Metering Device as the refrigerant enters an Evaporator Coil of an HVAC system:
The Metering Device takes liquid and then reduces the ...
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What value should I use for P in the ideal gas equation for an unknown molar quantity?
I did a chemistry lab, in which baking soda and vinegar were reacted in a ziplock bag, and I was to calculate the proper quantity of reactants to fill the bag with CO2. The molar quantity of gas was ...
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Applying vacuum at the end of a flash chromatography column
I know that flash chromatography uses a positive or pushing pressure to achieve the goal which is separation. Would the same goal be achieved if you had a vacuum on the other end instead of a ...
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Gas Law - increasing temperature with constant volume held
I've set up a simple experiment to look at the ideal gas laws. My experiment is relatively simple in that I have a metal tube which is capped on one side. I am then pressurising the tube with air to ...
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How can equilibrium lie to one side ? Surely it’s not at equilibrium anymore? [closed]
Surely they’re not at equilibrium any more?
I understand that a favourable condition can make a reaction in one direction go faster, but then surely either the forward or backward reaction is faster ...
