Enthalpy change is also known as heat of reaction, enthalpy of reaction, change in heat content.

Enthalpy = total energy of a system

It is impossible to measure the total kinetic and potential energy of a system, so instead we measure enthalpy change (using calorimeters).

Enthalpy Change –  is the energy absorbed from or released to the surroundings when a system changes from reactants to products.  It is given the symbol, DH.

DH = DHproducts DHreactants

DH is measured at STP or SATP for allowance of comparisons between enthalpy changes.

This idea is consistent with the law of conservation of energy, therefore;

Enthalpy change of system  =  quantity of heat that flows from system to  surroundings or vice versa

In other words;

DH  = ± q (DH= Delta H- Enthalpy Change)

Sign of DH

Endothermic Reaction:

  • System has absorbed heat energy from surroundings
  • Hproducts >  Hreactants
  • DH = Hproducts –  Hreactants

= positive value

  • DH is positive

Exothermic Reaction:

  • System releases heat energy into surroundings
  • Hproducts < Hreactants
  • DH = Hproducts –  Hreactants

= negative value

  • DH is negative
Cite this article as: William Anderson (Schoolworkhelper Editorial Team), "Enthalpy Change," in SchoolWorkHelper, 2019, https://schoolworkhelper.net/enthalpy-change/.

If we have helped you, please help us fix his smile with your old essays...it takes seconds!

-We are looking for previous essays, labs and assignments that you aced!

-We will review and post them on our website.
-Ad revenue is used to support children in developing nations.
-We help pay for cleft palate repair surgeries through Operation Smile and Smile Train.

Inline Feedbacks
View all comments