Energy Diagrams Cont:

The main point is to look at the diagram and to find the potential energy with quick simple calculations. You also have to determine whether it’s endothermic or exothermic.

Potential energy: added energy to create reaction whether released or absorbed.

Terms:

If you look to the diagrams in the previous blogs, you can find all the terms mentioned below. These terms will explain further of what happens in the diagram and what happens to the energy as the reaction proceeds.

·         Energy of Reactants (or just ‘reactants’ on the diagram): the ‘starting’ amount of energy of the diagram

·         Energy of Products (or just ‘products’ on the diagram): The result of the final product of the reaction with the given amount of energy.

·         ∆H: the change in potential energy (or enthalpy) it is given when to calculate the energy of products minus the energy of the reactant (Hprod – Hreact). It is switch to addition if trying to find the Hprod or Hreact out of the ∆H.

·         Energy of the Activated Complex: the transition of potential energy through reactants a products. To find it you must add the activation energy to the reactant.

·         Activation Energy: a ‘must-be’ added energy to continued reaction process. To find it you must minus the activated complex with the reactant.

*A thing about the diagrams, you can tell if the diagram is endothermic or exothermic by simply noticing where the Products line ends up; if it is higher than the Reactants line it is endothermic and vice-versa.*

Now On To Energy Calculations!

The energy is represented in KJ per mole in the chemical equation, and yes you heard it right, the MOLES are back. Which means it is added to the chart of mole equations, and how do you do that exactly? Well by:          (∆H) KJ                        1mol of (chosen element)

                                               1mol of (chosen element)                  (∆H) KJ         

*note: ∆H is not a constant number like in most mole equations so expect different amounts of energy in the reactions.*

-depending on where the ∆H is placed in the reaction, you can tell whether it is endothermic or exothermic, for example:               4C(s) + 6H(g) + O2(g)  à 2C2H5OH(l) + 470 KJ

Because the 470KJ is placed on the right side of the reaction it is exothermic, if on the other side it is endothermic. Let’s use this example again to show how the mole equation works: Calculate the amount of energy released when 1.50 moles of carbon is reacted:                                                   

4C(s) + 6H(g) + O2(g)  à 2C2H5OH(l) + 470 KJ

1.50 mole C x        470KJ     =  176.25 KJ energy released

                            4mol of C

*note: that you must always say ‘Energy Released’ as your final answer, also if the number is negative, by saying that; it gets rid of it for you, lessening confusion.*

-some equations can get a bit complex by asking for grams or molecules, but it should be no different from previous uses of mole equations, they are set up the same way so there should be no difficulty as we have already done them.