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Understanding Vapor Pressure: Temperature and Intermolecular Forces, Summaries of Chemistry

The concept of vapor pressure, its relationship with temperature and intermolecular forces, and how it impacts boiling points. It covers volatile and non-volatile liquids, the role of atmospheric pressure, and provides examples and exercises.

What you will learn

  • How does atmospheric pressure impact boiling?
  • Why do volatile liquids have low boiling points?
  • Which factors influence vapor pressure?

Typology: Summaries

2021/2022

Uploaded on 09/12/2022

edmond
edmond 🇺🇸

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VaporPressure2016.notebook
1
November02,2016
Nov72:39PM
Vapor Pressure
Aim: Toexaminev aporpressureasitrelatestotemperature
and intermolecularforcesofattraction.
Nov72:39PM
VaporPressure –thepressureexertedbygasmolecules
(vapor)abovethesurfaceofaliquidasitevaporates.
Vaporpressureincreasesasthe
liquidevaporates intoagasmore
rapidly.
Increasingtemperaturecausesmoreevaporationand
anincreaseinthevaporpressurebecausemoreliquid
particlesescapeasagas
.
2factorsthatinfluencevapor pressure:
Temperature
Intermolecularforcesofattraction
H
2
O(l)
H
2
O(g)
Vapor
Pressure
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pf4
pf5

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Nov 72:39 PM

Vapor Pressure

Aim: To examine vapor pressure as it relates to temperature

and intermolecular forces of attraction.

Nov 72:39 PM

Vapor Pressure – the pressure exerted by gas molecules

(vapor) above the surface of a liquid as it evaporates.

Vapor pressure increases as the

liquid evaporates into a gas more

rapidly.

Increasing temperature causes more evaporation and

an increase in the vapor pressure because more liquid

particles escape as a gas.

2 factors that influence vaporpressure:

Temperature

Intermolecular forces of attraction

H 2 O (l) H 2 O (g) Vapor Pressure

Nov 72:39 PM

  • Volatile^ Liquids^ have^ weak intermolecular forces (acetone, gasoline, paint) and evaporate very easily, and have a high vapor pressure.
  • These^ liquids^ have^ low boiling points because attractions are very weak.
  • BP ethanol = 79 °C

Intermolecular Forces, Evaporation,

Vapor Pressure, and Boiling Point

  • Liquids^ with^ strong intermolecular forces (water) do not evaporate easily and have very low vapor pressure.
  • These^ liquids^ have^ high boiling points because more energy is needed to overcome particle attractions.
  • BP^ water=^100 °C

WEAK ATTRACTIONS STRONG^ ATTRACTIONS

Substances with strong intermolecular forces of attraction between particles will have a low vapor pressure due to low evaporation and a high boiling point because a lot of energy is needed to go from a liquid to a gas due to the strong attractions. Nov 72:39 PM Vapor Pressure & Boiling

Atmospheric pressure The

pressure pushing down on the

surface of a liquid.

This pressure interferes with

evaporation (liquid particles

can't escape as easily) and

therefore it is more difficult to

boil.

Two ways to get a liquid to boil: 1)Increase the temperature in order to increase the vapor pressure. 2)Decrease the atmospheric pressure until it equals the vapor pressure.

A liquid will only boil when the vapor pressure of the

liquid is equal to the atmospheric pressure.

Atmospheric Pressure Vapor Pressure

Nov 72:39 PM

  1. What is the vapor pressure of water at 105°C?
  2. At which temperature would ethanol have the highest vapor pressure? a. 30°C b. 50°C c. 40°C d. 60°C
  3. What is the normal boiling point of ethanoic acid?

120 kPa

117 kPa

Nov 21:05 PM

Water boils at 100 °C on Long Island where the atmospheric

pressure is 101.3 kPa. Water boils at 95 °C in Denver

Colorado where the atmospheric pressure is 91 kPa.

Explain why water has a higher boiling point on Long island

than in Colorado?

The atmopsheric pressure is higher on Long Island

therefore more energy is required to allow water to

boil because the vapor pressure must be higher for

liquid to escape as a gas than in Colorado.

Nov 72:39 PM

Water on Long Island boils at 100°C while in Denver, CO water

boils at 95°C.

This is because the atmospheric pressure is lower in Denver

and it requires less energy to get the vapor pressure of the

liquid to overcome the atmospheric pressure on a mountain

than at sea level.

http://www.youtube.com/watch?v=VjgfelzQ_aE