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# Heat of formation

Standard heat of formation or standard enthalpy change of formation. How heats of formation are calculated.  Created by Sal Khan.

## Want to join the conversation?

• what does 'enthalpy' mean in the bigger picture? What does it do for the system?
• Enthalpy is similar to energy. It can be thought of as energy in most cases. In all honesty, enthalpy is a broader term than energy because it accounts for pressure and volume in addition to all that energy accounts for. Its a state function of the system. Thus, it doesn't "do" anything. Its just a quantity in a system.
• how is energy released? i mean in exothermic.. heat is given out ? how?
• Chemical energy is stored in every bond and atom it is that energy that is changed into thermal
• is the heat of formation the same thing as the heat of reaction?
• sorry but i would like to quote that heat of formation is only equal to heat of reaction in cases where compounds are formed directly from its elements.but when comounds are formed from compounds there is heat of reaction but is it heat of formation i guess no it is equal to differnce in hp-hr
• Does anyone else have suggestions for other enthalpy/calorimetry videos and practice problems? I found this to be even more confusing, and I still don't understand it.
• read a book first and then see this video i understand it that way
• What is difference between heat and temperature?
• Temperature is the average kinetic energy of the particles of the system whereas
Heat is the quantity of energy that flows across the boundary of a system during a change in its state due to the difference in temperature between the system and the surroundings.
• I would like to ask why the heat when released is 74kJ and not -74kJ, I thought when heat is released, it would be an exothermic process, so shouldn't it be negative?
• deltaH is -74kJ but when you write that in a equation in the left side it is written as +74kJ as it is a product of the reaction "heat is evolved "
• How do you tell whether an equation is endothermic or exothermic? For example what would C2H4 yields 2C t 2H2 + 52.3 kJ
• In the equation q=mc∆T , is q equal to ∆H?
• Yes, if the experiment is done under conditions of constant pressure. If the pressure is not held constant, then q is not equal to ∆H.
• Sal says 1/2 mole of O2. Is that possible? Can you break a n atom or a molecule into two and consider it as two equal parts?