Worksheet: The Second Law of Thermodynamics

In this worksheet, we will practice defining the second law of thermodynamics, which states that the entropy of the universe must increase.

Q1:

Which of the following represents a necessary condition for a chemical reaction to proceed from reactants to products spontaneously?

  • AThe reaction must be exothermic.
  • BThe total entropy of the reacting chemical system and its surroundings must increase.
  • CThe reaction must be endothermic.
  • DThe standard entropy change, Δ𝑆, for the chemical reaction must be 0.

Q2:

Which of the following played a significant role in developing the concept of entropy and in formulating the second law of thermodynamics?

  • AThe Nernst heat theorem
  • BThe equipartition of energy principle
  • CThe Heisenberg uncertainty principle
  • DThe formulation and analysis of the Carnot cycle and heat engine

Q3:

Which of the following statements does not conform to the laws of thermodynamics?

  • AThe entropy of any chemically pure substance approaches a value of zero as the temperature of the substance approaches a value of 0 K and at 𝑇=0K and 𝑆=0.
  • BThe entropy of a system always decreases with a decrease in the temperature of the system.
  • CThe entropy of the universe always increases in a spontaneous change of state process.
  • DThe energy of the universe always remains constant in any change of state process.

Q4:

In which of the following processes is the change in the entropy of the system most negative?

  • A P b S ( ) P b ( ) + S ( ) s a q a q 2 + 2
  • B 2 H O ( ) 2 H ( ) + O ( ) 2 2 2 l g g
  • C 2 N a ( ) + 2 H C l ( ) 2 N a C l ( ) + H ( ) s g s g 2
  • D 2 C H ( ) + 1 9 O ( ) 1 4 H O ( ) + 1 2 C O ( ) 6 1 4 2 2 2 l g g g
  • E Z n ( ) + 2 H N O ( ) Z n ( N O ) ( ) + H ( ) s a q a q g 3 3 2 2

Q5:

In which of the following processes is there a decrease in the entropy of the materials involved?

  • AOxidation of iron in air
  • BCombustion of butane
  • CDecomposition of hydrogen peroxide into water and oxygen
  • DBoiling of ethanol
  • EWarming of ice to near its melting point

Q6:

Why is it difficult to predict whether the entropy change in the complete combustion of methane will be positive or negative?

  • AThe products of the reaction vary depending on the oxygen concentration.
  • BThe reactants and products can all be modeled as ideal gases.
  • CThe reaction does not change the number of covalent bonds.
  • DHeat released by the reaction may reverse the sign of the entropy change.
  • EThe reaction does not change the number of gaseous molecules.

Q7:

The melting of ice is represented by the equation HO()HO()22sl. The standard molar entropy change for this process is 22.1 J/K⋅mol and each mole of water absorbs 6.012 kJ from the surroundings. Calculate the change in the entropy of the universe when 1.00 mole of ice melts at 10C.

Q8:

The boiling of water is represented by the equation HO()HO()22lg. The standard molar entropy of a material, 𝑆, is the molar entropy of the material at 298 K and 1.00 bar pressure. The value of 𝑆 for liquid water is 70.0 J/mol⋅K and the value for steam is 188.8 J/mol⋅K. Calculate Δ𝑆, the standard molar entropy change for boiling water.

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