Which of the following statements regarding spontaneous changes is false?A. Spontaneity is favored when heat is released.B. Spon
1 answer:
Answer: Option (E) is the correct answer.
Explanation:
A spontaneous reaction is defined as the process which tends to occur on its own. And, a non-spontaneous reaction is defined as a process for the completion of which we have to provide certain conditions.
For example, ice melting at is spontaneous primarily due to the increase in molecular disorder (dispersal of matter). Also, melting of ice is taking place on its own without any external force.
It is not necessary that all exothermic reactions will be exothermic in nature.
Thus, we can conclude that the statement all exothermic reactions are spontaneous, is false.
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The number of moles of reactants and products can be used to obtain the mass of products formed. The results obtained are as follows;
- The mass of hydrogen produced is 0.0174 grams
- The mass of zinc produced is 0.5688 grams
- The percentage by mass of zinc in the brass alloy is 47.3 %
The question says that HCl was in excess. It means that after the reaction, we will have unreacted HCl(aq) and ZnCl2(aq) in the remaining solution.
Hence;
Mass of ZnCl2(aq) formed = 36.309g - 35.123g = 1.186g
Number of moles ZnCl2(aq) formed =
= 0.0087 moles
From the reaction equation;
To obtain the amount of Zn reacted
1 mole of Zn yields 1 mole of ZnCl2
x moles of Zn yields 0.0087 moles of ZnCl2
x = 0.0087 moles of Zn
a) 1 mole of Zn yields 1 mole of H2
0.0087 moles of Zn yields 0.0087 moles of H2
Mass of H2 = 0.0087 moles of H2 * 2 g/mol = 0.0174 grams
b)
Mass of Zn reacted = 0.0087 moles of Zn * 65.38 grams/mole = 0.5688 grams
c)
Percentage of Zn in the alloy = 0.5688 grams/1.203g * 100 = 47.3 %
Answer:
The rate constant of an SN1 reaction depends on the nucleophile
The rate constant of an SN2 reaction does not depend on the nucleophile
Explanation:
Let us recall that in an SN1 reaction, the rate determining step involves only the alkyl halide substrate and not the nucleophile. Hence;
Rate = k[RX]
Therefore;
k= Rate/[RX]
For an SN2 reaction, the rate determining step involves both the nucleophile and the alkyl halide substrate.
Hence;
Rate = k[Nu-] [RX]
k= Rate/[Nu-] [RX]
Note that;
[Nu-] = concentration of the nucleophile
[RX] =concentration of alkyl halide substrate
k= rate constant
We can see from the above derivations that;
1) The rate constant of an SN1 reaction does not depend on the nucleophile
2) The rate constant of an SN2 reaction depends on the nucleophile
