Gases and Kinetic Molecular Theory

This PowerPoint will cover Properties of Gases Definition of Kinetic Molecular Theory Definition of Temperature Explanation of the Kelvin Scale Definition of Gas Pressure Units of Pressure

Three Phases of Matter

Solids *Molecules are tightly packed. *High intermolecular forces. *Molecules are vibrating in place. *Have a fixed shape and volume.

Liquids Molecules are packed. Intermediate intermolecular forces. Molecules are moving around. Have a fixed volume but takes shape of its container.

Gases Molecules are far apart. No intermolecular forces. Molecules are moving around a lot. No fixed volume (can be compressed) nor shape (takes shape of container).

Gas Properties – more details Volume – a gas does not have a definite shape or volume. The volume depends on the container size, room temperature and pressure. Expandability- gases will expand to fit any size container. Increasing temperature will cause the gas to expand thereby increasing volume and pressure in the container.

Compressibility- the volume of a gas can be decreased by increasing the pressure.

Gases are Air heads! Low Density- because the particles in a gas are so far apart and density is mass per unit volume, it makes sense that gases occupy roughly 1000 times more volume than the same amount of substance as a liquid or solid. Gases are mostly empty space!

Diffusion is the spontaneous mixing of the particles of two different gases.

Kinetic-Molecular Theory (KMT) 1) Gases consist of tiny particles (atoms or molecules) that are far apart relative to their size. The particles have an insignificant volume 2) Gas particles are in constant random motion. More energy = faster particles

3) There are no forces of attraction or repulsion between the particles. 4) Collisions between gas particles and between particles and the container are elastic. (no net loss of kinetic energy).

5) The average kinetic energy of gas particles depends on the temperature of the gas. Higher temperature means more energy and faster particles

What is temperature? Temperature is a measure of the kinetic energy of molecules.  The faster molecules are moving, the higher the temperature. High temperature Low temperature

What is heat? A. Heat is the total energy of molecular motion in a substance (while temperature is a measure of the average energy of molecular motion in a substance.) B. Heat energy depends on the speed of the particles, the number of particles (the size or mass), and the type of particles in an object. (Temperature does not depend on the size or type of object. )

For example, the temperature of a small cup of water might be the same as the temperature of a large tub of water, but the tub of water has more heat because it has more water and thus more total thermal energy. High temperature but low heat Low temperature but high heat

Units of Heat Calories – used to measure energy of food Joules BTU (British Thermal Units) – used for heaters

Units of Temperature Celsius ( 0 C) – based on the freezing and boiling point of water  O 0 C = Water freezes  C = Water boils Temperature is measured with a thermometer

KELVIN (SI unit of temperature) Since temperatures on the Celsius scale can be negative (colder than the freezing point of water) scientists created another scale based on the Celsius scale and that is the Kelvin Scale. There are some formulas in which you have to divide by the temperature, which doesn’t work if the temperature is a negative number.  ° C = K − 273 or K =°C So 0 °C = 273 K

Absolute Zero is the lowest possible temperature, at which point the atoms are completely at rest. It is 0 degrees on the Kelvin scale, which translates to -273 degrees Celsius.temperature Absolute zero is the lowest temperature that could ever be. In fact, it's so low that we can never quite reach it, although research teams have come within a fraction of a degree.

Pressure Gas Pressure is created by the collisions of gas particles with a surface. In general – more collisions = higher pressure and less collisions = lower pressure

Units of Pressure Kilopascal (KPa) Millimeters of Mercury (mmHg)  Pressure that supports a 1mm mercury column in barometer.  How blood pressure is measured.

Units of Pressure Atmosphere (atm) Torr  Another name for millimeters of mercury  1 torr = 1mmHg PSI (pounds per square inch)  Used for tire pressure So at sea level, standard pressures of air are 1 atm =760 mm Hg =760 torr = kPa (kilopascal) =14.7 psi (standard temperature is 0 0 C)

Pressure Conversions 400 torr = _____ atm? 400 torr 1 atm = 0.53 atm 760 torr