#### Heats of Reaction: Screencasts

Explains how to determine heats of reaction at 298 K from heats of formation and how to calculate heats of reaction at elevated temperatures.

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

Explains Hess’s law and provides an example of how to use it to solve for the heat of reaction for an equation.

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

Uses Hess’s law to show how heat of combustion is used to calculate the heat of reaction.

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

##### Important Equations:

$\Delta H_{rxn} = \sum \nu_i \Delta H_{f,i}$

where $$\Delta H_{rxn} =$$ heat of reaction at 298 K, $$\nu_i =$$ stoichiometric coefficient for component $$i$$, and $$\Delta H_{f,i} =$$ heat of formation (enthalpy of formation) or species $$i$$ at 298 K.

$\Delta H_{reaction,T} = \Delta H_{reaction,298} + \int^{T}_{298} \Delta C_P\,dT$

Heat capacity (J/(mol K)) can be of the form

$C_{P,i} = A_i + B_iT + C_iT^2 + D_iT^3$

where $$C_{P,i}$$ is the heat capacity of component $$i$$, $$A_i, B_i, C_i, \,and\, D_i$$ are the constants for the heat capacity equation for component $$i$$, and $$T$$ is temperature in Kelvin.

$\Delta C_P = \sum \nu_i C_{P,i}$

$\Delta H_{reaction,T} = \Delta H_{reaction,298} + \sum \nu_i A_i (T-298 + \frac{\sum \nu_i B_i}{2}(T^2-298) + \frac{\sum \nu_i C_i}{3}(T^3 -298^3) +\frac{\sum \nu_i D_i}{4}(T^4-298)$

$\Delta H_{reaction,T} = \Delta H_{C,reactant}^{\circ} – \sum \Delta H_{C,product}^{\circ}$

where $$\Delta H_{C,reactant}^{\circ}$$ is the heat of combustion of a reactant at standard states, and $$\Delta H_{C,product}^{\circ}$$ is the heat of combustion of a product at standard states.