Gases and vapours Flashcards
What happens at a molecular level when evaporation occurs?
Some molecules have a kinetic energy that is greater than the force of attraction to surrounding molecules so will break free. Heat increases this process.
What is saturated vapour pressure?
The pressure exerted by vapour in equilibrium with a liquid at a certain temperature. Occurs when liquid is stored in an enclosed place.
Is the relationship between SVP and increasing temperature linear or non-linear?
Non linear, it is a slight upward curve
What happens when SVP reaches atmospheric pressure?
The substance boils and 100% becomes vapour
How is SVP related to ambient pressure?
Ambient pressure (pressure of surrounding medium) doesn’t effect SVP.
However, as boiling point occurs when SVP meets atmospheric pressure, more vapour will be present with decreased ambient pressure due to boiling. SVP is unaffected, but partial pressure of the gas vapour will increase.
What happens if you try and make a cup of tea on Everest?
Decreased BP due to decreased pressure.
Therefore, it might not have a chance to brew the tea, prior to the water turning to vapour.
What is the BP, SVP and MAP of desfluorane?
BP (degrees C at atm) = 23
SVP (at 20 deg c) = 88.5
MAC 6.0
What is the BP, SVP and MAP of sevo?
BP (degrees C at atm) = 59
SVP (at 20 deg c) = 21.3
MAC = 2.0
What is the BP, SVP and MAP of iso?
BP (degrees C at atm) = 48
SVP (at 20 deg c) = 32
MAC = 1.15
What is the BP, SVP and MAP of enflurane?
BP (degrees C at atm) = 56.5
SVP (at 20 deg c) = 23
MAC = 1.68
What is the BP, SVP and MAP of halothane?
BP (degrees C at atm) = 50.2
SVP (at 20 deg c) = 32.5
MAC = 0.75
What is latent heat?
The heat energy used to cause a phase change
More vigorous molecules have enough energy to escape to gas phase and those left behind have a lower average energy. Therefore to vaporise, the liquid below is left colder.
What is latent heat of vaporisation?
Heat energy required to convert a liquid into vapour whilst maintaining the same overall temperature.
What is latent heat of fusion?
The heat energy required to change a solid into a liquid whilst maintaining the same overall temperature
Why do the temperatures not change is latent heat of vaporisation/fusion even when a constant heat is being applied?
The energy is being used to break/make bonds between molecules so is not used for overall warming/increasing the average kinetic energy.
I.e. heat is used to change the phase of the substance
What is the difference between heat and temperature?
Heat is energy whilst temperature is a measure of hot/coldness
How does latent heat of vaporisation vary with liquid temperature?
Water closer to BP will require less latent heat to achieve vaporisation than water at room temperature
What is specific latent heat?
The heat required to change one kg of a substance from one phase to another J/kg, must be quoted in reference to a temperature
What is the specific latent heat of water at 100 deg c and at body temperature?
100 = 2.26 mJ/kg
Body temp = 2.43
What is adiabatic change?
No heat is transferred to or from a system
And be achieved by using an insulated container or by a process being done quickly, so heat doesn’t have enough time to transfer.
What happens is we decompress a gas with an adiabatic process?
Gas expands and requires energy to overcome the VDW’s between molecules. As adiabatic no energy is gained from the environment and all energy is taken from the molecules internal energy, so the overall gas cools.
What happens is we compress a gas with an adiabatic process?
What is an example?
The temperature rises as pushing the molecules together increases the pressure and the kinetic energy (Joule Kelvin principle or joule Thomson effect)
Can occur if a cylinder attached to a machine is turned on too quickly. Can cause an explosion if combustibles around.
What is isothermal change?
If compression or expansion happens slowly, then there is time for heat loss/transfer, to/from the environment and so a state change occurs with no temperature change.
Why do we use vaporiser?
SVP’s of volatiles are higher than room temps and so we need a machine to mix fresh gas with some volatile in a reliable manner. The dial gives a splitting ratio e.g. splits the carrier gas between the volatile chamber and the gas outlet to deliver a controlled, predictable level of the anaesthetic agent, compared to the carrier gas.
