Question

SCHE 231 Chapter 6, Worksheet 1 Energy Diagrams 1. Why might it be important to understand the energy associated with a chemical reaction? What is this energy associated with? 2. Enthalpy What is Enthalpy (AH)? When is ΔΗ Positive? when is ΔΗ negative? In the diagram below, label which reaction is exothermic and which is endothermic Enthalpy 04) Enthalpy Sarting Products materials AN Starting materials Products Reaction coordinate Reaction coordnate

Answer 1

(1)It is important to understand the energy associated to a chemical reaction because when some compounds undergo the chemical reaction, there is absorption of energy takes place when the chemical bonds are broken or cleaved , and when during chemical reaction,the bonds are formed and this results in release of energy .

Hence we can conclude that a chemical reactions associated with the change in the energy between products(formed after completion of the chemical reaction) and reactants (participating in chemical reaction to give product).

According to the Law of Conservation of Energy, the total energy of a system must remain unchanged, so to balance the amount of energy on the reactant as well as the product side the chemical reaction may absorb or release any form of energy i.e heat or light .

(2)The heat content of the reactant and the product is known as the enthalpy of the reactant and the product respectively.The difference in the heat content of the reactants and the products is known as the enthalpy of the reaction.

• ΔH is symbolized as the change in enthalpy of a chemical reaction.

ΔH = H_p-H_R

where H_p = heat content of product; H_R = heat content of reactant

when the ΔH is positive ,it means that the heat content of product is more than that of the reactant ,i.e the product formed is less stable (According to law of thermodynamics we know that lower the heat content of the substance more is its stability).

when the ΔH is negative ,it means that the heat content of product is less than that of the reactant ,i.e the product formed is stable (According to law of thermodynamics we know that lower the heat content of the substance more is its stability).

• The graph on the left (showing that the product is having the lower energy than reactant) is for exothermic reaction (in which the release of energy takes place).

The graph on the right (showing that the product is having the higher energy than reactant) is for endothermic reaction (in which the absorption of energy takes place).

3) Entropy of the reaction is defined as the degree of the randomness in the reaction.

Change in entropy is defined as the amount of the energy absorbed per unit temperature(ΔS = Q/T)

• Entropy is affected by the amount of energy present in the system and the temperature of the system.,if more amount of energy is added to a system than the entropy is increased because the high amount of energy increases the randomness,in the same way Temperature on increasing temperature the randomness of the system increases .
• The open chain is having high value of entropy as all the bonds are free to rotate independently as all atoms are singly bonded, but the cyclic system has the lower value of entropy because it is more ordered due to the cyclic structure (hindered rotation)
• In the equation ΔS_total = ΔS _sys + ΔS _surr

ΔS_total = total entropy change for the process.

ΔS_sys = entropy change of the system.

ΔS_surr = entropy change of the surrounding.

• ΔS if positive it means that the reaction is spontaneous as according to laws of thermodynamics we know that entropy of any spontaneous reaction is always positive.
• For the given reaction we find that there more number of the moles of the products on the products side is present(i.e 2 moles) than that of the reactants(i.e 1 mole) , hence the randomness is increased so( as we know more is the number of the moles of the substance more is its randomness ,more is its entropy), ΔS is found to be positive,hence the reaction is spontaneous.

4)According to the equation given:

ΔG is negative than the reaction is spontaneous and the favours the product formation.

ΔG is positive than the reaction is non-spontaneous and the does not favours the product formation.

Exogonic reactions are those reactions in which the energy is released during the reaction ,i.e the energy of product is less than that of the energy of the reactant which is shown by the graph on the right side in the image.

Endogonic reactions are those reactions in which the energy is absorbed during the reaction ,i.e the energy of product is more than that of the energy of the reactant which is shown by the graph on the left side in the image.