Equation:	C8H18	+	O2		CO2	+	H2O
Balancing:	2 C8H18	+	25 O2		16 CO2	+	18 H2O
Stoichiometry (n or V):	2	:	25	:	16	:	18
Before reaction:	0.025 L		0.600 L		0		0
V octane required to react with 0.600 L oxygen = {2/25}{0.600 L} = 0.048 L, more than available, so octane limits; O2 = 0.600 - (25/2)(0.025) = 0.600-0.3125 = 0.288 L, From V octane can then find V CO2 = (16/2)(0.025) = 0.200 L and V H2O = (18/2)(0.025) = 0.225 L
After reaction:	0 L		0.288 L		0.200 L		0.225 L

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Kinetic Molecular Theory of Gases

Kinetic-molecular theory is a simple model to explain properties of gases. There are four basic postulates:

• A gas is composed of a large number of tiny particles (molecules, or atoms for the inert gases). These particles are so small that the sum of the particles volumes is negligible compared to the volume of their container - most of the container volume is empty space.

• The particles of a gas are in rapid, linear motion. They make frequent collisions with each other and the walls of any vessel containing them. All collisions between gas particles and between gas particles and container walls are elastic. (There is no net loss of kinetic energy in collision - energy can be exchanged between particles, but the total stays the same.)

• Except when they are colliding, the particles are completely independent of each other. That is, there are no forces of attraction or of repulsion between them.

• The particles in a gas have a wide range of velocities: some may be nearly still, while others move at great speed. Thus there is a wide range of kinetic energies in any gas. However, the average kinetic energy for any gas is the same at a given temperature. The average kinetic energy for the particles in a gas is proportional to the absolute temperature of the gas. (KE = 3/2 RT, R is still the Gas constant, but different units.)

© R A Paselk

Last modified 2 March 2015