The quantity of energy associated with the formation of one mole of a substance from its elements (in their standard states).

The standard states (at SATP) of most elements is solid, except for the gaseous diatomic molecules, H2, O2, N2, F2, Cl2, and the two liquid elements Hg and Br2.

These energies can be looked up in standard tables and have the units, KJ/mol.

Writing Formation Reactions:

  • Write one mole of the product in the state that has been specified on the product side.
  • Write the reactant elements in their standard states on the ((
  • Balance the equation for only one mole of product.

For example:

Write the formation reaction for glucose, C6H12O6(s).

C(s) +     H2(g) +   O2(g) →     C6H12O6(s) ΔH°f = -1273.1KJ/mol

Now, balance the equation for one mole of glucose produced.

6C(s) +     6H2(g) +   3O2(g) →     C6H12O6(s)

The standard state for elements in their standard states is zero.

READ:
Enthalpy Change

For example;

Br2(l) Br2(l) ΔH°f = 0

The enthalpy change for any equation (target equation) equals the sum of the enthalpies of formation of the products minus the sum of the enthalpies of formation of the reactants.

ΔH  =  ∑nΔH°f(products) –  ∑nΔH°f(reactants)

Note:  Each of the product and reactants is multiplied by the number of moles of each in the equation (target equation).

Cite this article as: William Anderson (Schoolworkhelper Editorial Team), "Standard Enthalpies of Formation," in SchoolWorkHelper, 2019, https://schoolworkhelper.net/standard-enthalpies-of-formation/.

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.

guest
0 Comments
Inline Feedbacks
View all comments