Topic: Entropy
Entropy
Which equation represents a change that results in an increase in disorder?
(1) I2(s) → I2(g)
(2) CO2(g) → CO2(s)
(3) 2Na(s) + Cl2(g) → 2NaCl(s)
(4) 2H2(g) + O2(g) → 2H2O(ℓ)
Which term is defined as a measure of the randomness of a system?
(1) heat
(2) entropy
(3) pressure
(4) temperature
The arrangement of particles is most ordered in a sample of
(1) NaCl(aq)
(2) NaCl(ℓ)
(3) NaCl(g)
(4) NaCl(s)
During which phase change does the entropy of a sample of H2O increase?
(1) H2O(g) → H2O(ℓ)
(2) H2O(g) → H2O(s)
(3) H2O(ℓ) → H2O(g)
(4) H2O(ℓ) → H2O(s)
Given the balanced equation representing a reaction:
2H2O(ℓ) + 571.6 kJ → 2H2(g) + O2(g)
What occurred as a result of this reaction?
(1) Energy was absorbed, and entropy increased.
(2) Energy was absorbed, and entropy decreased.
(3) Energy was released, and entropy increased.
(4) Energy was released, and entropy decreased.
Which term is defined as a measure of the disorder of a system?
(1) heat
(2) entropy
(3) kinetic energy
(4) activation energy
Entropy is a measure of the
(1) acidity of a sample
(2) disorder of a system
(3) concentration of a solution
(4) chemical activity of an element
The amount of randomness of the atoms in a system is an indication of the
(1) entropy of the system
(2) polarity of the system
(3) excited state of the atoms
(4) ground state of the atoms
Which phase change results in an increase in entropy?
(1) I2(g) → I2(s)
(2) CH4(g) → CH4(ℓ)
(3) Br2(ℓ) → Br2(g)
(4) H2O(ℓ) → H2O(s)
Which term represents the disorder of a system?
(1) entropy
(2) mole
(3) quanta
(4) pressure
When ice, H2O(s), melts at 0°C, entropy increases because the
(1) average kinetic energy of the particles increases
(2) average kinetic energy of the particles decreases
(3) particle arrangement is more random
(4) particle arrangement is less random
The compounds KNO3 and NaNO3 are soluble in water.
Compare the entropy of 30. grams of solid KNO3 at 20.°C with the entropy of 30. grams of KNO3 dissolved in 100. grams of water at 20.°C.
Allow 1 credit. Acceptable responses include, but are not limited to:
• The entropy of KNO3(s) is less than the entropy of KNO3(aq).
• The KNO3(aq) is more disordered.
• The solution is more random than the solid.
• Note: Do not allow credit for a response that only indicates the entropies are different.
The balanced equation below represents the reaction of glucose, C6H12O6, with oxygen at 298 K and 101.3 kPa.
C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(ℓ)
Compare the entropy of the reactants to the entropy of the products.
Allow 1 credit. Acceptable responses include, but are not limited to:
• The entropy of the reactants is less than the entropy of the products.
• The reactants are more ordered.
• The products have greater entropy.
Hydrazine, N2H4, is a compound that is very soluble in water and has a boiling point of 113°C at standard pressure. Unlike water, hydrazine is very reactive and is sometimes used as a fuel for small rockets. One hydrazine reaction producing gaseous products is represented by the balanced equation below.
N2H4(ℓ) → N2(g) + 2H2(g) + heat
Compare the entropy of the products to the entropy of the reactant for this reaction.
Allow 1 credit. Acceptable responses include, but are not limited to:
• The gaseous products have greater entropy than the liquid reactant.
• The products are more disordered.
A few pieces of dry ice, CO2(s), at −78°C are placed in a flask that contains air at 21°C. The flask is sealed by placing an uninflated balloon over the mouth of the flask. As the balloon inflates, the dry ice disappears and no liquid is observed in the flask.
Compare the entropy of the CO2 molecules in the dry ice to the entropy of the CO2 molecules in the inflated balloon.
Allow 1 credit. Acceptable responses include, but are not limited to:
• The CO2 molecules in the dry ice have less entropy than the CO2 molecules in the inflated balloon.
• The CO2 gas in the balloon is more disordered.
• less for CO2(s)