Change in Heat equations

[Riya Prabhakar 3B]

If we are not given the value for the change of heat, what are the different equations we can use to solve for it?

[ishankhurana2D]

Hi! If not given the value for change in heat, you can use the enthalpies of formation (Delta H_f) to calculate the Delta H value. Furthermore, if you know the change in enthalpy values for two chemical reactions who can be combined to achieve the one you desire, you can manipulate these reactions by changing the direction of the reaction or multiplying the reaction by coefficients and changing the delta H value accordingly (if you multiply the reaction by a coefficient, you multiply the delta H value by the same coefficient, and if you change the direction of the reaction, you change the sign (+ or -) of delta H.

[Yixin Wu 3B]

To add to the calculation with enthalpies of formation (Delta H_f), the enthalpy of formation is a measure of the energy released or absorbed when one mole of a substance is created under standard conditions from its pure elements. A chemical reaction usually involves the breaking down of reactants (opposite to Delta H_f) and forming of molecules (same sign as Delta H_f). As a result, the formula for calculating the enthalpy of a reaction is the sum of all Delta H_f of products minus the sum of all Delta H_f of reactants.