The power needed to drive a certain fan can be computed as follows:
where Q is the fan volume in m3/h and P is the total discharge pressure in cmH2O.
a. What is the corresponding unit of the formula constant?
b. Transform the formula to compute power in horsepower (hp), using fan volume in ft3/min and pressure in inH2O.
The rate of a chemical reaction r (or c t^-1) is given by:
r = k [A]^a x [B]^b
where k is the rate constant, A and B are the concentrations of the two reactants and the exponents a and b are integers and give the order of the reaction. The overall kinetic order is the summation of a and b.
If we apply units where c is the concentration in moles or mass per litre, then,
c t^-1 = k x c^a x c^b,
or k = ct^-1/(c^a x c^b)
Therefore the units of the rate constant depend on the kinetic order of the reaction. Assuming the various possibilities of 0, 1, 2 or 3 for the orders will determine the units of k.
For a first order involving one chemical entity, the unit of k is ct^-1/(c^1) or t^-1.