give enthalpy profile diagrams to illustrate endothermic and exothermic reactions. include an explanation of cocepts such as enthalpy change, activation energy and catalysts.explain how the process of bond breakage and formation determine the enthalpy change of a reaction giving suitable equation with data for each.
Enthalpy profile diagrams are graphical representations that show the energy changes that occur during a chemical reaction. They can illustrate both endothermic and exothermic reactions.
1. Endothermic Reaction:
An endothermic reaction is a reaction that absorbs heat energy from the surroundings. In an enthalpy profile diagram, this is shown by the products having a higher energy level than the reactants. Here is an example of an endothermic reaction:
Reactants: A + B
Products: C + D
^
|
Energy |
| C
| B /
| /
| /
| / D
| /
| A
|
------------------->
Reaction Progress
In this diagram, the reactants (A and B) have a lower energy level compared to the products (C and D). The energy difference between the reactants and products is the enthalpy change (∆H), which is positive for endothermic reactions.
2. Exothermic Reaction:
An exothermic reaction is a reaction that releases heat energy to the surroundings. In an enthalpy profile diagram, this is shown by the products having a lower energy level than the reactants. Here is an example of an exothermic reaction:
Reactants: E + F
Products: G + H
^
|
Energy |
| G
| F \
| \
| \
| \ H
| \
| E
|
------------------->
Reaction Progress
In this diagram, the reactants (E and F) have a higher energy level compared to the products (G and H). The energy difference between the reactants and products is the enthalpy change (∆H), which is negative for exothermic reactions.
Now, let's discuss some important concepts related to enthalpy change, activation energy, and catalysts:
Enthalpy Change (∆H): It is the difference in energy between the products and the reactants. For an endothermic reaction, ∆H is positive, indicating that energy is absorbed. For an exothermic reaction, ∆H is negative, indicating that energy is released.
Activation Energy: It is the minimum amount of energy required for a chemical reaction to occur. In an enthalpy profile diagram, the activation energy is represented by the energy barrier between the reactants and the transition state (highest point on the graph).
Catalysts: Catalysts are substances that speed up the rate of a reaction by lowering the activation energy, without being consumed in the process. They provide an alternative reaction pathway with a lower activation energy barrier. Catalysts do not affect the enthalpy change of a reaction.
Bond Breakage and Formation: During a chemical reaction, chemical bonds are broken in the reactants and new bonds are formed in the products. The energy required to break bonds is absorbed (endothermic), and the energy released when new bonds are formed is released (exothermic). The net energy difference determines the overall enthalpy change of the reaction.
For example, consider the reaction between methane (CH4) and oxygen (O2) to form carbon dioxide (CO2) and water (H2O):
CH4 + 2O2 -> CO2 + 2H2O (∆H = -890 kJ/mol)
In this reaction, four C-H bonds in methane are broken (endothermic) and two O=O bonds in oxygen are also broken. Simultaneously, two C=O bonds and four O-H bonds are formed (exothermic) in CO2 and H2O, respectively. The net energy change (∆H) for this reaction is -890 kJ/mol, indicating that it is an exothermic reaction.