heats-of-reaction-screencasts

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.

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

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

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Important Equations:

$Δ H_{r x n} = \sum ν_{i} Δ H_{f, i}$

where $Δ H_{r x n} =$ heat of reaction at 298 K, $ν_{i} =$ stoichiometric coefficient for component $i$ , and $Δ H_{f, i} =$ heat of formation (enthalpy of formation) or species $i$ at 298 K.

$Δ H_{r e a c t i o n, T} = Δ H_{r e a c t i o n, 298} + \int_{298}^{T} Δ C_{P} d T$

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

$C_{P, i} = A_{i} + B_{i} T + C_{i} T^{2} + D_{i} T^{3}$

where $C_{P, i}$ is the heat capacity of component $i$ , $A_{i}, B_{i}, C_{i}, a n d D_{i}$ are the constants for the heat capacity equation for component $i$ , and $T$ is temperature in Kelvin.

$Δ C_{P} = \sum ν_{i} C_{P, i}$

$Δ H_{r e a c t i o n, T} = Δ H_{r e a c t i o n, 298} + \sum ν_{i} A_{i} (T - 298 + \frac{\sum ν_{i} B_{i}}{2} (T^{2} - 298) + \frac{\sum ν_{i} C_{i}}{3} (T^{3} - 298^{3}) + \frac{\sum ν_{i} D_{i}}{4} (T^{4} - 298)$

$Δ H_{r e a c t i o n, T} = Δ H_{C, r e a c t a n t}^{\circ} - \sum Δ H_{C, p r o d u c t}^{\circ}$

where $Δ H_{C, r e a c t a n t}^{\circ}$ is the heat of combustion of a reactant at standard states, and $Δ H_{C, p r o d u c t}^{\circ}$ is the heat of combustion of a product at standard states.

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Heats of Reaction: Screencasts

Important Equations: