Unit 3: States of aggregation

Unit 3 States of aggregation

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Kinetic Molecular Theory and Postulates

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Pressure

Pressure is a derived quantity. Force exerted on a unit of surface. Its unit in the SI is the pascal (Pa) Pascal: Force exerted by one newton on a surface of one square meter 1 Pa = 1 N/m²

Pressure

When walking in the snow, the footprints left when wearing boots are much deeper than when walking with snowshoes. This is because the force exerted by our feet on the snow is the same in both cases, but the area of the snowshoes is larger than that of the boots, so the pressure will be lower in the case of snowshoes.

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Snow and pressure

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Pressure

Why do some tractors and construction machinery have tracks instead of wheels? Explain it using what you have learned about pressure.

Pressure: Gas

Gas enclosed in a container with rigid walls. This gas exerts pressure on the container. Pressure is related to:

• Intensity of the particle movement
• High pressure: Greater movement and number of collisions between particles .

Atmospheric Pressure

Pressure exerted by the mass of air forming the atmosphere on the Earth's crust and on all the material systems it contains is called atmospheric pressure.

• Value decreases with altitude
• At sea level, atmospheric pressure has a value of 101,300 Pa.

Atmospheric Pressure

Other units (non SI):

• Atmospheres (atm)
• Bars (bar)

Equivalences 1 atm = 101325 Pa 1,013 bar = 101300 Pa 1 bar = 100000 Pa

pressure

Calculate the following pressures atm:

• 101325 Pa
• 90000 Pa

• 1,017 bar
• 998 bar

Calculate the following pressures in bar:

• 101325 Pa
• 1,2 atm
• 100000 Pa

Calculate the following pressures in Pa:

• 1,2 atm
• 0,99 atm
• 1,080 bar

Temperature

Also explained using the Kinetic Molecular Theory (KMT). Temperature is a fundamental quantity, and its unit in the SI is the kelvin (K). When we increase the temperature of a material system, the kinetic energy of its particles also increases.

Temperature

Melting temperature: temperature at which both melting and solidification occur. Boiling temperature: temperature at which the state change of vaporization occurs throughout the entire mass of the liquid (boiling) The melting and boiling temperatures are characteristics of each substance; therefore, they are specific properties that allow us to differentiate one substance from another.

Temperature Scales

inStrument: Thermometer

• Digital
• Mercury
• Colored alcohol

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Temperature Scales

Celsius scale: divided into one hundred units between the melting and boiling points of water. Water Melting point 0ºC Water Boiling point 100ºC Kelvin scale: Water Melting point 273K Water Boiling point 373 K

Temperature Scales

Temperature

Calculate the following temperatures in Kelvin:

• 0ºC
• 100ºC

• 125ºC
• 450ºC
• -15ºC
• -85ºC
• 600ºC

Calculate the following temperatures in Celsius:

• 273K
• 373 K
• 125K
• 100K
• 0K
• 14K
• 89K

Ideal gases laws

The laws of ideal gases demonstrate the relationship between pressure, volume, and temperature of a gas. To observe how one of these three quantities (dependent magnitude) varies, another is kept constant (controlled magnitude), and the third one (independent magnitude) is varied.

Ideal gases laws

• Boyle and Mariotte's Law.
• First Law of Charles and Gay-Lussac.
• Second Law of Charles and Gay-Lussac.

Ideal gases laws

• Boyle and Mariotte's Law.
• First Law of Charles and Gay-Lussac.
• Second Law of Charles and Gay-Lussac.

Boyle and Mariotte's Law.

• We keep the temperature constant during the process.
• We vary the volume and observe what happens with the pressure. We record the values we obtain.

CONCLUSIONS The mathematical relationship between pressure and volume is inversely proportional: p · V = constant    p1 · V1 = p2 · V2

Boyle and Mariotte's Law.

SIMULATOR BLINKLEARNING What happens when you increase volume? What happens when you increase temperature? How is the density of the gas affected?

Ideal gases laws

• Boyle and Mariotte's Law.
• First Law of Charles and Gay-Lussac.
• Second Law of Charles and Gay-Lussac.

First Law of Charles and Gay-Lussac.

Pressure is constant

SIMULATOR BLINKLEARNING

Ideal gases laws

• Boyle and Mariotte's Law.
• First Law of Charles and Gay-Lussac.
• Second Law of Charles and Gay-Lussac.

second Law of Charles and Gay-Lussac.

Volume is constant

SIMULATOR BLINKLEARNING

Unit 3 States of aggregation

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