States of Matter Chapter 13

Kinetic Theory All of matter is constantly moving.

Kinetic Theory All of matter is constantly moving. The energy of motion is called “kinetic energy” – Particles (molecules or atoms) are like tiny spheres. – In a gas they bounce everywhere at about 1000 miles per hour! But they bounce off each other, and around randomly, not really going that fast. They bounce elastically (like bouncy balls).

Gas Pressure As those particles bounce, they hit against things with a force. Force in an area is called pressure So, the force of a gas in an area is called “Gas Pressure” – An area with no particles (and therefore no pressure or mass) is called a vacuum.

Atmospheric Pressure The mass of the air on Earth is pulled down by gravity, creating force and pressure – Called “atmospheric pressure”. – Measured by a barometer. Used to be a tube of mercury in a bowl of mercury, and the air pushed the mercury up the tube. Higher pressure = taller mercury column

Standard Pressure The original standard pressure (pressure at sea level) was a height of 760 mm – about 30 inches tall. – Also called “One atmosphere” The new (SI) measurement is a pascal (Pa) – But a pascal is really, really small, so instead they normally used 1000 pa (or 1 kPa) – Standard pressure is 101.3kPa

Pressure Conversions 760 mm = 1 atm = kPa Same as any other conversion. 1.Write down the measurement you want to convert 2.Put the unit and number of the measurement you have in the denominator 3.Put the unit and number you want in the numerator. 4.Multiply across and divide.

Let’s try one… How many kilopascals (kPa) are in 720 mm of mercury?

Try these. How many mm of mercury are in 4.00 atm? How many atm are in 320 kPa?

Measuring Kinetic Energy Every particle has a speed, and therefore a measurable kinetic energy – Some particles have more, and some have less, and it’s impossible to figure out exactly how much each one has – So, instead, we measure the AVERAGE kinetic energy

properties properties

Temperature is Kinetic Energy Temperature is a measure of the average kinetic energy, with 0 Kelvin being no energy. Molecules with double the kelvin temperature has double the amount of energy.

MFo MFo

Liquids are cool, too. Liquids are like gasses – They are both fluid, as they flow But they are a little more “stuck together” and can’t escape each other like gasses “Attractive forces” hold them together. – Hydrogen bonds, Van der Waals bonds, and dipole forces – Don’t bounce, but kind of slide by each other. Liquids have less energy than gasses, so they can’t run away.

Vaporization Vaporization is the name of the process of when a liquid changes to a gas. – Can be boiling (when heat is applied to vaporize) Outside heat gives the atoms enough energy to escape. – Or evaporation (which happens where the liquid meets a gas) Evaporation is when an individual atom gets enough energy to “escape” the liquid, and become a gas.

Vapor Pressure – When a liquid is in an open container it can evaporate and leave the container. In a sealed container, the liquid turns into a gas, and then pushes – Just like gas pressure, but since the particle is usually a liquid, it’s called “vapor pressure” Gas pressure = gasses at room temp. Vapor pressure = liquids at room temp. – The vapor pressure eventually balances out (equilibrium), and the pressure stays the same. (Equal number leave as come back.)

Temperature and Vapor Pressure As temperature goes up, more atoms will leave the liquid, and become a gas. – That means MORE vapor pressure. (They want to get away faster, and more.) The vapor pressure can be measured by using a U- shaped tube, and seeing how high the mercury (or other liquid) will go.

Boiling Point Boiling Point is the temperature at which the particles throughout a substance will vaporize – It is actually the temperature at which the pressure outside the liquid is LESS than the vapor pressure of the liquid At that specific temperature Normal boiling point is the boiling point (BP) at 1 atm.