Question

For each hypothetical scenario below, state whether ∆???? is > 0, < 0, or approximately 0. Also state if ∆???? is > 0, < 0, or approximately 0. Then, based on your analysis, decide if the process is always spontaneous, never spontaneous, if it depends on temperature, or if more information is necessary.

a. When two molecules combine and make one new molecule, the reaction vessel becomes warm.

b. Two small beakers of liquid are mixed, resulting in lots of bubbling and the escape of a large amount of gas. As this occurs, the temperature of the liquid and the bubbles increases—hot to the touch!

c. Molecule A decomposes all on its own to form only molecule B. The temperature of the vessel remains the same.

d. A beaker with one compound is set above a Bunsen burner, which heats it up. As it warms, the compound decomposes and forms two new molecules.

Answer 1

a. When two molecules combine and make one new molecule, the reaction vessel becomes warm.

Here, vessel become warm that means heat is released.It is an exothermic reaction.so enthalpy of reaction is negative i.e. ∆???? is <0

Entropy: It is the measurement of randomness.

Now, here two molecules combine and make one new molecule which means randomness decreases . Hence change in entropy for this reaction is negative i.e. ∆???? is < 0

As the change in entropy is negative so the process is non spontaneous(never spontaneous)

b. Two small beakers of liquid are mixed, resulting in lots of bubbling and the escape of a large amount of gas. As this occurs, the temperature of the liquid and the bubbles increases—hot to the touch!

Here beaker become hot after mixing two liquid that means heat is released .It is an exothermic reaction.Hence, enthalpy of reaction is negative i.e. ∆???? is <0. Minus sing indicate heat is released.

Now, order of randomness:-

Gas>liquid>solid

Here after mixing of two liquid huge amount of gas bubbles formed. Randomness of gas is more than liquid. So entropy increase i.e.∆???? is >0 (positive)

Therefore the process is always spontaneous.

c. Molecule A decomposes all on its own to form only molecule B. The temperature of the vessel remains the same.

As the temperature of the vessel remains the same so, ∆???? is approximately 0.

Note : ∆????= ∆?product - ∆Hreactant

Now, A molecules becomes B. So ∆Srxn is approximately 0. Hence reaction is always spontaneous.

Note: for spontaneous reaction ∆Srxn should be greater than or equal to zero.

d. A beaker with one compound is set above a Bunsen burner, which heats it up. As it warms, the compound decomposes and forms two new molecules.

Here to complete the reaction the heat was supplied to the Reactant first,that means heat was absorbed by the reactant. It is an endothermic reaction. So, enthalpy of reaction is positive i.e. ∆???? is >0.

As the one compound decomposes and forms two new molecules, hence the randomness increases which leads to increase in entropy. Hence change in entropy for this reaction is positive i.e. ∆???? is >0

Therefore reaction is always spontaneous.