Energy Balances with Reaction: Screencasts

For a chemical reactor energy balance, explains the terms for the approach that uses the heat of reaction and extent of reaction. This approach uses reactants and products at 25°C and 1 atm as reference states.

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

For a chemical reactor energy balance, this screencast explains the terms for the approach that uses enthalpies of reactants and products that are calculated based on elements as reference states.

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

Important Equations:

Energy balance using heat of reaction (reference states are reactants and products at 25°C and 1 atm)

$\xi\Delta\dot{H}^{\circ}_{reaction} + \Sigma\dot{n}_{i,out} H_{i,out}\, -\, \Sigma\dot{n}_{i,in} H_{i,in} + \Delta\dot{E}_{K.E.} + \Sigma\dot{E}_{P.E.} = \dot{Q} + \dot{W}_S$

where $$\xi$$ = extent of reaction (dimensionless) = $$(\dot{n}_{i,out} – \dot{n}_{i,in})/\nu_i$$

$$\nu_i$$ = stoichiometric coefficient (positive for products, negative for reactants)

$$\Delta\dot{H}^{\circ}_{reaction}$$ = $$\Sigma\nu_i\,\Delta H^{\circ}_{f,i}$$

$$\dot{n}_{i,out}$$ = molar flow rate of component $$i$$ out of system (mol/s)

$$\dot{n}_{i,in}$$ = molar flow rate of component $$i$$ into system (mol/s)

$$H_{i,out}$$ = enthalpy of component $$i$$ exiting the system, relative to its enthalpy at a reference temperature (J/mol)

$$H_{i,in}$$ = enthalpy of component $$i$$ entering the system, relative to its enthalpy at a reference temperature (J/mol)

$$\Delta\dot{E}_{K.E.}$$ = change in kinetic energy of system per time (J/s)

$$\Delta\dot{E}_{P.E.}$$ = change in potential energy of system per time (J/s)

$$\dot{Q}$$ = heat added (J/s)

$$\dot{W}_S$$ = shaft work added (J/s)

Energy balance using heats of formation (reference states are elements at 25°C and 1 atm)

$\Sigma\dot{n}_{i,out} H_{i,out}\, -\, \Sigma\dot{n}_{i,in} H_{i,in} + \Delta\dot{E}_{K.E.} + \Sigma\dot{E}_{P.E.} = \dot{Q} + \dot{W}_S$

Note that enthalpies are defined differently from above.

where $$H_{i.out}$$ = enthalpy of component $$i$$ exiting the system, relative to the enthalpy of its elements at a reference temperature (J/mol)

$$H_{i,in}$$ = enthalpy of component $$i$$ entering the system, relative to the enthalpy of its elements at a reference temperature (J/mol)