Topic: Entropy
Entropy
Entropy is a measure of
(1) accuracy
(2) precision
(3) the disorder of a system
(4) the attraction of a nucleus for an electron
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)
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)
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 term is defined as a measure of the randomness of a system?
(1) heat
(2) entropy
(3) pressure
(4) temperature
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
Which term is defined as a measure of the disorder of a system?
(1) heat
(2) entropy
(3) kinetic energy
(4) activation energy
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 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)
Systems in nature tend to undergo changes toward
(1) lower energy and less randomness
(2) higher energy and less randomness
(3) lower energy and greater randomness
(4) higher energy and greater randomness
In terms of disorder and energy, systems in nature have a tendency to undergo changes toward
(1) less disorder and lower energy
(2) less disorder and higher energy
(3) greater disorder and lower energy
(4) greater disorder and higher energy
Fruit growers in Florida protect oranges when the temperature is near freezing by spraying water on them. It is the freezing of the water that protects the oranges from frost damage. When H2O(ℓ) at 0°C changes to H2O(s) at 0°C, heat energy is released. This energy helps to prevent the temperature inside the orange from dropping below freezing, which could damage the fruit. After harvesting, oranges can be exposed to ethene gas, C2H4, to improve their color.
Explain, in terms of particle arrangement, why the entropy of the water decreases when the water freezes.
Allow 1 credit. Acceptable responses include, but are not limited to:
• The arrangement of the H2O(ℓ) molecules is more random than the H2O(s) molecules.
• The molecules in ice have a rigid, orderly arrangement.
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.
Explain, in terms of particle arrangement, why a sample of solid NaCl has less entropy than a sample of aqueous NaCl.
Allow 1 credit. Acceptable responses include, but are not limited to:
• Solid NaCl has less entropy because the particles have a more ordered arrangement than aqueous NaCl.
• NaCl(aq) is a mixture that contains water molecules and ions moving more randomly.
• Particle arrangement in NaCl(s) is less random.
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.