GIVE ENTHALPY PROFILE DIAGRAMS TO ILLUSTRATE ENDOTHERMIC AND EXOTHERMIC REACTIONS.INCLUDE AN EXPLANATION OF CONCEPTS SUCH AS ENTHALP CHANGE, ACTIVATION ENERGY AND CATALYSIS. EXPLAIN HOW THE PROCESSES OF BOND BREAKKAGE AND FORMATION DETERMINE THE ENTHALPY CHANGE OF A REACTION GIVING SUITABLE EQUATION WITH DATA FOR EACH.
We can't do diagrams on the board AND this is a discussion question. Obvously the text/teacher wants YOUR input and not ours.
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To illustrate endothermic and exothermic reactions, let's start by understanding the concept of enthalpy change. Enthalpy change (ΔH) is the amount of heat transferred during a chemical reaction. It represents the difference in energy between the products and reactants.
An exothermic reaction releases energy in the form of heat, resulting in a decrease in the enthalpy of the system. On the other hand, an endothermic reaction absorbs heat energy from the surroundings, leading to an increase in the enthalpy of the system.
Enthalpy profile diagrams, also known as reaction coordinate diagrams or energy level diagrams, plot the energy changes throughout a chemical reaction.
Now, let's consider an endothermic reaction: the decomposition of calcium carbonate (CaCO3) into calcium oxide (CaO) and carbon dioxide (CO2):
CaCO3(s) → CaO(s) + CO2(g)
In this reaction, energy must be absorbed to break the chemical bonds in the calcium carbonate. This process requires energy due to the breaking of bonds, resulting in an increase in the overall enthalpy of the system. The enthalpy profile diagram for this endothermic reaction would look like this:
ENERGY
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Reactants |
└─⇧─ Activation Energy (∆H ↑)
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Products
The activation energy (∆H ↑) represents the minimum energy required to initiate the reaction. In this case, it is the energy needed to break the bonds in CaCO3.
In contrast, let's consider an exothermic reaction: the combustion of methane (CH4) in the presence of oxygen (O2) to produce carbon dioxide (CO2) and water (H2O):
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
In this reaction, energy is released when the chemical bonds are formed in the products. This results in a decrease in the overall enthalpy of the system. The enthalpy profile diagram for this exothermic reaction would look like this:
ENERGY
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Reactants |
─⇩─ Activation Energy (∆H ↓)
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Products
The activation energy (∆H ↓) represents the minimum energy required to initiate the reaction. In this case, it is the energy needed to break the bonds in CH4.
Now, let's discuss the role of catalysis in a chemical reaction. Catalysts are substances that increase the rate of a reaction without being consumed themselves. They achieve this by providing an alternative pathway with a lower activation energy.
For example, in the decomposition of hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2):
2H2O2(aq) → 2H2O(l) + O2(g)
The decomposition of hydrogen peroxide is slow in the absence of a catalyst. However, the presence of the catalyst, such as manganese dioxide (MnO2), lowers the activation energy of the reaction, making it faster. The enthalpy profile diagram with catalysis would look like this:
ENERGY
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Reactants |
─── Catalyst Effect
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Products
The catalyst provides an alternative pathway for the reaction, reducing the activation energy required and facilitating the formation of the products.
In summary, enthalpy profile diagrams illustrate the energy changes in chemical reactions. Endothermic reactions require energy to break bonds and show an increase in enthalpy. Exothermic reactions release energy during bond formation and exhibit a decrease in enthalpy. Activation energy represents the minimum energy required to initiate a reaction, which can be influenced by catalysts.