Gases flashcards

• 1. Gases are compressible - The volume of a gas decreases dramatically when pressure is exterted on the gas because molecules are spaced further apart in gases than in liquid.
• 2. Gases expand as the temperature is increased - If pressure remains constant because the molecules are moving faster/have more kinetic enrgy.
• 3. Gases have low viscosity (low resistance to flow) - Gases flow through pipes more freely than liquid such as water. Gases will escape quickly through small openings in their containers.
• 4. Gases have much lower densities than solids or liquids - There is more space between molecules.
• 5. Gases are miscible - They mix completely and evenly with each other when put in the same container.

• Pressure is the amount of particle collisions per area. It increases with temperature and compression.
• Kinetic molecular theory (KMT) provides a scientific model for explaining the behaviour of gases.

An Ideal gas is a hypothetical gas that obeys all gas laws perfectly under all conditions. A Real gas deviates from an ideal gas under certain conditions. Real gases behave very nearly like ideal gases at relatively low pressures and high temperatures, such as STP and SATP conditions.

KMT ideal gas assumption	Real gas interpretation
Gas molecules are very far apart compared to their size. In other words molecule size is negligible.	For high pressures the molecules are forced much closer together and their size becomes significant - The empty space availible is less than the size of the container
Molecules are in constant, random straight line motion because no forces exist between them.	As temp. decreases the molecules slow down. At some point, the intermolecular attractions may cause the molecules to stick together and the gas to become a liquid.
Gas molecules undergo perfectly elastic collisions in which no energy is lost and collisions and rebounds occur very quickly - hard molecule model	Molecules of a real gas are more like soft sphere. Shape change during collision and rebound makes the process occur a little more slowly. This means that the pressure of the gas is a little less than ideal and energy is lost as heat.

• Gas pressure is a measure of the force exterted by moving gas molecules per unit area. It is specific to a gas.
• Atmospheric pressure is the force per unit area exterted by air on all objects. Air is made up of O2, N2, H2, CO2, CH4 and SO2 and NO2.

Unit	Symbol	Conversion
Pascal (si unit)	Pa	1 Pa = 1N/m^2
atmosphere	atm	1 atm= 101.325 kPa
milimeters of mercury	mm Hg	760 mm Hg = 1 atm = 101.325 kPa
torricelli	torr	1 torr = 1mm Hg

Temperature is a measure of the avg kinetic energy of particles; the more kinetic energy the particles have, the higher the temperature. Heat is a measure of the total kinetic energy.

The absolute temp. scale (kelvin) is commonly used in chemistry. Absolute zero (0k or -273.15 degrees celsius) is the the lowest possible temperature, at this temp the kinetic energy of all entities would theoretically become zero. It is represented by a capital T, while Celsius temp is a lowercase t.

Celsius to kelvin: T=t + 273.15, Kelvin to celsius: t=T - 273.15

• STP is standard temp and pressure and it is 273.15k (0 degrees celsius) and 100kPa.
• SATP is standard ambient temp and pressure (SATP) and it is defined as 298.15k (25 degrees celsius) and 100kPa.

These are standard sets of conidtions for experimental measurements that allow comparisons between different sets of data.

Lussac's law of combining volumes states that when measures at the same temperature and pressure, volumes of gaseous reactants and products of chemical reactions are always in simple ratios of whole numbers. These #'s match the whole # ratios by the coefficients of a balanced chemical equation. Avogadro's law provides the reasoning for this, equal volumes of gases at the same temp and pressure contain equal numbers of molecules.

V(req)= V(given) x coefficient(req)/coefficient(given)

Boyle's law states that as the pressure on a gas increases, the volume od the gas decreases porportionally, provided that the temp and chemical amount of gas remain cosntant. This means volume is inversely porportional to pressure. Increasing pressure makes gas molecules closer decreasing volume, Decreasing the volume results in more frequent collisions between gas molecules and container, increasing pressure.

Volume vs Pressujre graphs will be non linear, showing an inverse relationship between volume and pressure. Volume vs the inverse of pressure graphs and vise versa while be linear. *Be aware of this on the test. Boyle's law's formula is p1v1=p2v2. It must be noted that when using this formula any units of pressure and volume can be used as long as the SAME units are used for all, meaning conversions may need to happen.

Charles's law states that as temperature of a gas rises, volume increases porportionally as long as the pressure and chemical amount of the gas remain constant. If the gas did not liquify, at absolute zero the kinetic enrgy of all entities would theoretically become zero, thus zero volume (ideal gas law - molecule size is negligable). 

The formula for this law is that V1/T1=V2/T2. For this formula any units of pressure can be used as long as it is the same unit for all measurements but temp must be in kelvin.

It states that the product of the pressure and volume of a gas sample is porportional to its absolute temp in kelvin. Chemical amount must remain constant. The equation is P1V1/T1=P2V2/T2. When using this formula temp must be in kelvin and all units of measurement must be the same for all measurements. If a variable remains constant it can be eliminated from the combined gas law equation.

• The ideal gas law describes the interrelationship of pressure, temp, volume and chemical amount of matter - the four variables that define a gaseous system. The laws that this law combines are boyles law (volume is inversely porportional to pressure), charles' law (volume is porportional to abs temp), Avogradro's law (volume of a gas is directly porportional to the chemical amnt of matter). This gives us the equation PV = nRT.
• P = pressure in kpa, V = volume in litres, n = chemical amount in mol, R is the universal gas constant (8.314 kPaL/molK) and T is temp in kelvin. 
• The formula n=m/M is used to convert between chemical amnt and mass