Chemistry 231 . Introduction and Gases . Physical Chemistry. Physics - study of the properties of matter that are shared by all substances Chemistry - the study of the properties of the substances that make up the universe and the changes that these substances undergo
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Introduction and Gases
Physics - study of the properties of matter that are shared by all substances
Chemistry - the study of the properties of the substances that make up the universe and the changes that these substances undergo
Physical Chemistry - the best of both worlds!
Thermodynamics – the study of energy and its transformations
Thermochemical changes – energy changes associated with chemical reactions
open system ® exchanges mass and energy
closed system ® exchanges energy but no mass
isolated system ® no exchange of either mass or energy
Metastable - the progress towards the equilibrium state is slow
Equilibrium state - state of the system is invariant with time
Reversible transformation - the direction of the transformation can be reversed at any time by some infinitesimal change in the surroundings
Irreversible transformation - the system does not attain equilibrium at each step of the process
Gas - a substance that is characterised by widely separated molecules in rapid motion
Mixtures of gases are uniform. Gases will expand to fill containers.
The pressure of a gas is best defined as the forces exerted by gas on the walls of the container
Define P = force/area
The SI unit of pressure is the Pascal
1 Pa = N/m2 = (kg m/s2)/m2
Defines the gas volume/temperature relationship.
V T (constant pressure and amount of gas)
Note T represents the temperature on the absolute (Kelvin) temperature scale
t / C
(-273C = 0 K)
Lord Kelvin – all temperature/volume plots intercepted the tc axis at -273.15°C).
Kelvin termed this absolute 0 – the temperature where the volume of an ideal gas is 0 and all thermal motion ceases!
The pressure/temperature relationship
For a given quantity of gas at a fixed volume, P T, i.e., if we heat a gas cylinder, P increases!
The volume of a gas at constant T and P is directly proportional to the number of moles of gas
V n => n = number of moles of gas
An ideal gas is a gas that obeys totally the ideal gas law over its entire P-V-T range
Ideal gases – molecules have negligible intermolecular attractive forces and they occupy a negligible volume compared with the container volume
Let's consider two ideal gases (gas 1 and gas 2) in a container of volume V.
In the limit of low pressures
The Isothermal Compressibility
The coefficient of thermal expansion