Scelta multipla
For a reaction to be spontaneous at all temperatures, the signs of ΔH and ΔS must be:
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19. Chemical Thermodynamics
Spontaneous vs Nonspontaneous Reactions
Scelta multipla
The process of iron being oxidized to make iron(III) oxide (rust) is spontaneous. Which of these statements about this process is true?
A
The reduction of iron(III) oxide to iron is also spontaneous.
B
The oxidation of iron is an endothermic process.
C
Because the process is spontaneous, the oxidation of iron leads to a decrease in Gibbs free energy.
D
The formation of rust is a nonspontaneous process under standard conditions.
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Understand the concept of spontaneity in chemical reactions: A spontaneous process is one that occurs naturally under given conditions without external intervention. It is often associated with a decrease in Gibbs free energy (ΔG).
Recall the relationship between Gibbs free energy and spontaneity: For a process to be spontaneous, the change in Gibbs free energy (ΔG) must be negative. This indicates that the system is releasing energy and moving towards a more stable state.
Consider the oxidation of iron to form iron(III) oxide: This is a spontaneous process, meaning ΔG < 0. Therefore, the statement 'Because the process is spontaneous, the oxidation of iron leads to a decrease in Gibbs free energy' is true.
Evaluate the other statements: The reduction of iron(III) oxide to iron is not spontaneous under the same conditions because it would require an input of energy, making ΔG > 0. The oxidation of iron is not endothermic; it is exothermic, releasing energy as heat.
Understand the conditions for spontaneity: The formation of rust is spontaneous under standard conditions, contradicting the statement 'The formation of rust is a nonspontaneous process under standard conditions.'
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