Think and Compare: 9.43 Part A Rank the following in order of increasing entropy

Question

Think and Compare: 9.43

Part A

Rank the following in order of increasing entropy. A deck of playing cards

Rank following from lowest entropy to highest entropy.

at 45 °C, new and unshuffled sitting in a room at 25 °C.

at 233 °C, new and unshuffled sitting in a room at 25 °C.

at 25 °C, used and shuffled sitting in a room at 25 °C.

Part B

The yeast in bread dough feeds on sugar to produce carbon dioxide. Why does the dough rise faster in a warmer area?

The yeast in bread dough feeds on sugar to produce carbon dioxide. Why does the dough rise faster in a warmer area?

The rate of evaporation increases with increasing temperature.

Part C

Rank the following reaction profiles in order of decreasing reaction speed.

Rank reaction profiles from fastest to slowest.

at 45 °C, new and unshuffled sitting in a room at 25 °C.

at 233 °C, new and unshuffled sitting in a room at 25 °C.

at 25 °C, used and shuffled sitting in a room at 25 °C.

Explanation / Answer

Part A

The entropy of a system increases with molecular motions as well as with temperature. The deck of card will have the lowest energy when they are new and unshuffled at 25°C; when the temperature is increased to 45°C, the entropy increases; however, there are no molecular motions and hence, the entropy doesn’t increase significantly.

When the temperature is increased from 25°C to 233°C, the entropy increases greatly. Hence, the entropy is higher than that in the first case.

When the deck of cards is used and shuffled, molecular motions are induced in the cards and hence, this system will have the highest entropy. Thus the order of increasing entropy is

At 45°C, unused and unshuffled < At 233°C, unused and unshuffled < At 25°C, used and shuffled.

Part B

The dough rises faster in warm conditions since there are more collisions. The higher the temperature of the system, the greater is the random motion of molecules. Consequently, the chances of molecular collisions increases and hence, the chances of reaction increases. Thus, the number of effective collisions increase with temperature and hence the reaction rate increases.

Part C

In the first reaction profile, the energy of the products is lower than the energy of the reactants; consequently, G < 0 and the reaction proceeds spontaneously. However, the activation energy of the reaction is high. The activation energy is the difference in energy between the transition state and the reactants. The higher the activation energy, the more difficult is the reaction and consequently, the reaction rate drops.

In the second profile, the reactants and the products have comparable energies. Thus, G will have a low negative value. The activation energy is low however; hence, the reaction proceeds at a fast pace.

In the third reaction profile, the reactants have lower energy than the products. Consequently, G > 0 and the reaction is non-spontaneous. A non-spontaneous reaction proceeds very slowly unless catalysts are used.

Therefore, the order of reaction profiles from fastest to slowest is

2nd picture > 1st picture > 3rd picture.

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