Unit 6: Topic 2 - Energy Diagrams Flashcards
What is an energy diagram?
An energy diagram shows the amount of potential energy in each step of a chemical reaction.
What are the components of an endothermic energy diagram?
In an single-step endothermic reaction, the
potential energy of the products is higher than
that of the reactants, implying that energy is
added to the system. Therefore, the enthalpy
change (delta H) is positive. The reactants form an
activated complex, an unstable arrangement of
atoms, that exists momentarily at the high-energy
transition state. The difference of the potential
energy of the activated complex and the potential
energy of the reactants is the activation energy.
What are the components of an exothermic energy diagram?
In an single-step exothermic reaction, the
potential energy of the products is lower than
that of the reactants, implying that energy is
released from the system. Therefore, the
enthalpy change (delta H) is negative. The reactants form
an activated complex, an unstable arrangement of
atoms, that exists momentarily at the high-energy
transition state. The difference of the potential energy of
the activated complex and the potential energy of the
reactants is the activation energy.
Using the energy diagram, determine the following:
a) What is the potential energy of the reactants?
b) What is the potential energy of the products?
c) What is the change in enthalpy (delta H)?
d) What is the activation energy?
e) Is this an endothermic or exothermic reaction?
a) 40 kJ
b) 20 kJ
c) -20 kJ (the difference of the potential energy of products and the potential energy of reactants)
d) 60 kJ (the difference of the potential energy of the activated complex at the transition step and the potential energy of the reactants)
e) exothermic (there is a negative change in enthalpy, which means that energy is released during this reaction; potential energy of reactants is greater than potential energy of products)
