LearnChemE

Chemical Reactions: Screencasts

Defines the term fractional conversion.

We suggest that after watching this screencast, you list the important points as a way to increase retention.

Demonstrates how to use the percent yield in order to determine the amount of theoretical reagents needed in a reaction.

We suggest that after watching this screencast, you list the important points as a way to increase retention.

Important Equations:

$Selectivity = \frac{n_D}{n_U}$

where $$n_D$$ is the moles of desired product formed, and $$n_U$$ is the moles of undesired product formed. Note that other definitions of selectivity are also used.

$Yield = \frac{n_D}{n_{D,max}} * 100%$

where $$n_{D,max}$$ is the moles of desired product that would form if all the limiting reactant were consumed and no undesired reactions occurred.

For a batch reactor:

$\xi = \frac{n_i – n_{i0}}{\nu _i}$

where $$\xi$$ is the extent of reaction (dimensionless) – note that many textbooks define $$\xi$$ so that it has unites of moles, $$n_i$$ is the number of moles of component $$i$$ at any time, $$n_{i0}$$ is the number of moles of component $$i$$ initially, and $$\nu _i$$ is the stoichiometric coefficient of component $$i$$.

$\xi = \frac{\dot n _i – \dot n _{i0}}{\dot{\nu} _i}$

where $$\dot n _i$$ is the molar flow rate of component $$i$$, $$\dot n _{i0}$$ is the molar flow rate of component $$i$$ at reactor inlet, and $$\nu _i$$ is the stoichiometric coefficient of component $$i$$ per time.

$f = \frac{n_{i0} -n_i}{n_{i0}} = \frac{\dot n _{i0} – \dot n _i}{\dot n _{i0}}$

where $$f$$ is the fractional conversion of component $$i$$.

$K = \Pi P^{\nu _i} _i$

where $$K$$ is the equilibrium constant for a gas-phase reaction, $$P_i$$ is the partial pressure of species $$i$$, and $$\Pi$$ represents a product (e.g., for reaction A + 2B $$\rightarrow$$ C, $$K = \frac{P_C}{P_A P^2 _B}$$