Which of the following determines whether molecules react spontaneously?
For a given reaction, the enthalpy and entropy changes are negative. The reaction is .
Calcium carbonate decomposes into calcium oxide and carbon dioxide gas: The standard entropies and enthalpies of formation for calcium carbonate and other materials are shown in the table.
|Material||Standard Molar Entropy (J/K⋅mol)||Standard Enthalpy of Formation (kJ/mol)|
All thermodynamic parameters are measured under a standard pressure of 1.000 bar. It may be assumed that the parameters do not vary significantly with temperature.
A sample of calcium carbonate is stored in an atmosphere of carbon dioxide at standard pressure. Calculate, to 3 significant figures, the minimum temperature in kelvin at which the sample would spontaneously decompose.
Calculate, to 1 significant figure, the equilibrium partial pressure of carbon dioxide when a sample of calcium carbonate is heated to .
A given reaction is non-spontaneous at all temperatures. Which of the following best accounts for this behavior?
For a given reaction, the enthalpy change is positive and the entropy change is negative. The reaction is .
For the process , occurring at a temperature of , the has a value of J/K⋅mol. Which of the following would reflect the values of and associated with the freezing of water at a temperature of ?
The standard enthalpy change for a reaction, , is 100 kJ/mol. The standard entropy change for the reaction is . It may be assumed that both quantities remain constant with varying temperature.
Calculate the minimum necessary value of for the reaction to be spontaneous at 298 K.
If , calculate the minimum temperature at which the reaction is spontaneous.
For a given reaction, the enthalpy and entropy changes are positive. The reaction is .
Which of the following processes are spontaneous?
Zinc reacts with solid copper sulfate to form copper and zinc sulfate. The standard entropies of these and other materials are shown in the table.
|Standard Molar Entropy||166.38||33.15||109.20||41.60||160.98||110.50|
Calculate, to 3 significant figures, the standard entropy change for this reaction, expressed per mole of zinc.
Calculate, to 3 significant figures, the maximum value of , the standard molar enthalpy change per mole of zinc, at which this reaction would occur spontaneously at 298 K.
Which of the following statements is false?
For a given reaction, the enthalpy change is negative and the entropy change is positive. The reaction is .
The standard entropies for two phases of sodium chloride are shown below:
|Standard Molar Entropy (J/K⋅mol)||72.11||95.06|
The standard enthalpy of fusion of sodium chloride, , is 27.95 kJ/mol.
Assuming that these thermodynamic parameters do not vary with temperature, estimate the melting point of sodium chloride to the nearest degree Celsius.
The observed melting point of sodium chloride is K. Which of the following is not a potential explanation for the difference between the observed and calculated melting temperatures?
A given reaction is spontaneous at high temperatures but not at low temperatures. Which of the following best accounts for this behavior?
A given reaction is spontaneous at low temperatures but not at high temperatures. Which of the following best accounts for this behavior?
The combustion of benzene produces carbon dioxide and water as the only products.
Write a balanced chemical equation for this reaction.
Predict the signs of the enthalpy change and entropy change for this reaction.
Why is heating necessary for this reaction to take place?
Why is the conversion of diamond to graphite not observed at room temperature and pressure?
Consider the following reaction for the decomposition of sodium bicarbonate: The and for this reaction have values of 85.2 kJ/mol and 215 J/K⋅mol, respectively. What is the minimum temperature required for an sample to spontaneously decompose into the products shown above (under 1 bar pressure conditions)?
What are the values of Gibbs free energy, , and the change in Gibbs free energy, , when a system reaches equilibrium?
A given reaction is spontaneous at all temperatures. Which of the following best accounts for this behavior?