qv and qp relationship Is there any relationship between q at constant volume and q at constant pressure that I could derive with just the reaction equation, and the enthalpy of formation and Cp of the products and reactants?
I am aware that q at constant pressure is enthalpy of formation of products - enthalpy of formation of reactants.
Let us assume that the initial and final temperatures in both the isobaric and isochoric processes are same. We will limit this discussion to ideal gases only. To calculate heat transfered we will use the expression $$q = nC\Delta T$$ Here C is molar heat capacity of the gas. For isobaric process, this will be $$q_p = nC_p\Delta T$$ For the isochoric process $$q_v=nC_v\Delta T$$
$\Delta T$ for both these processes same. Substracting these two equations we get $$q_p - q_v = n(C_p - C_v)\Delta T$$ The value of $C_p - C_v$ is $R$. Therefore $$q_p - q_v = nR\Delta T$$