1. Which is true about spontaneous reactions?
a. For a reaction to be spontaneous, Keq = 1.
b. Spontaneous reactions happen very rapidly.
c. A chemical reaction is spontaneous in both directions. ***
d. Spontaneous reactions do not require that anything be done to them.
2. At SATP, which reaction below is spontaneous?
a. CO2(s)→CO2(l)
b. CO2(s)→CO2(g) ***
c. CO2(g)→CO2(l)
d. CO2(l)→CO2(s)
3. For which system is ∆S<0?
a. CO2(g)→CO2(s) ***
b. CO2(s)→CO2(l)
c. CO2(s)→CO2(g)
d. CO2(l)→CO2(g)
4. Which pure substance under standard conditions would have the highest entropy?
a. H2O2(aq) ***
b. H2O(l)
c. H2O(s)
d. OH-(aq)
5. All the following involve a decrease in entropy except
a. condensation
b. crystallization
c. formation of a precipitate
d. diluting a weak base
***not sure about # 5.
I disagree with your choice for #1.
I think #5 is d. You increase "randomness" anytime you dilute something because there is more motion possible in a larger volume of solution.
1. would it be d, since spontaneous reactions occur naturally
I believe that is true.
1. To determine which statement about spontaneous reactions is true, we need to understand the concept of spontaneity in chemistry. Spontaneous reactions are those that occur naturally without the need for external intervention. Let's examine each statement:
a. For a reaction to be spontaneous, Keq = 1. This statement is incorrect. The equilibrium constant (Keq) can have various values for spontaneous reactions, including values greater than or less than 1.
b. Spontaneous reactions happen very rapidly. This statement is not necessarily true. The rate of a reaction (how quickly it occurs) is separate from whether it is spontaneous or not. Spontaneity only refers to the direction of the reaction.
c. A chemical reaction is spontaneous in both directions. This statement is correct. A spontaneous reaction can occur in both the forward and reverse directions, although one direction may be more favorable than the other.
d. Spontaneous reactions do not require that anything be done to them. This statement is correct. Spontaneous reactions proceed on their own without the need for external intervention or additional energy.
Therefore, the correct answer is c. A chemical reaction is spontaneous in both directions.
2. To determine which reaction is spontaneous at SATP (Standard Ambient Temperature and Pressure), we need to consider the phase changes involved. SATP represents a specific set of conditions with a temperature of 25 degrees Celsius and a pressure of 1 atmosphere.
a. CO2(s)→CO2(l) - This reaction involves the melting (solid to liquid) of carbon dioxide, which is generally non-spontaneous under normal conditions.
b. CO2(s)→CO2(g) - This reaction involves the sublimation (solid to gas) of carbon dioxide, which is spontaneous at SATP due to the low boiling point of CO2.
c. CO2(g)→CO2(l) - This reaction involves the condensation (gas to liquid) of carbon dioxide, which is generally non-spontaneous under normal conditions.
d. CO2(l)→CO2(s) - This reaction involves the freezing (liquid to solid) of carbon dioxide, which is generally non-spontaneous under normal conditions.
Therefore, the correct answer is b. CO2(s)→CO2(g).
3. To determine which system has a negative change in entropy (∆S<0), we need to consider the state changes involved.
a. CO2(g)→CO2(s) - This reaction involves the deposition (gas to solid) of carbon dioxide, which is a decrease in entropy as the particles become more ordered.
b. CO2(s)→CO2(l) - This reaction involves the melting (solid to liquid) of carbon dioxide, which is generally an increase in entropy as the particles become less ordered.
c. CO2(s)→CO2(g) - This reaction involves the sublimation (solid to gas) of carbon dioxide, which is generally an increase in entropy.
d. CO2(l)→CO2(g) - This reaction involves the vaporization (liquid to gas) of carbon dioxide, which is generally an increase in entropy.
Therefore, the correct answer is a. CO2(g)→CO2(s).
4. To determine which pure substance under standard conditions would have the highest entropy, we need to consider the nature of the substances.
a. H2O2(aq) - Hydrogen peroxide in aqueous solution has a higher entropy compared to its solid form, but it is not the highest entropy substance among the options.
b. H2O(l) - Liquid water has a lower entropy compared to its gaseous form.
c. H2O(s) - Solid ice has a lower entropy since the particles are more ordered.
d. OH-(aq) - Hydroxide ions in aqueous solution have a higher entropy compared to their solid form, but it is not the highest entropy substance among the options.
Therefore, the correct answer is a. H2O2(aq).
5. The question asks which of the following does NOT involve a decrease in entropy. To determine the correct answer, we need to understand that entropy generally increases with the random motion of particles and decreases with increases in order or organization.
a. Condensation - The phase change from gas to liquid involves a decrease in entropy, as the particles become more organized.
b. Crystallization - The formation of a crystalline solid involves a decrease in entropy since the particles become more ordered and arranged in a regular pattern.
c. Formation of a precipitate - This process involves the formation of a solid from a solution, which results in a decrease in entropy due to increased orderliness.
d. Diluting a weak base - Diluting a weak base involves mixing it with a solvent, which results in an increase in entropy as the molecules disperse and become more randomly distributed.
Therefore, the correct answer is d. Diluting a weak base, as it involves an increase in entropy rather than a decrease.