Chemical Kinetics in Environment Questions and Answers

Q: The following reaction is an example of CuCO3 → Cu + CO2

The reaction is a thermal decomposition.Heating copper(II) carbonate breaks it down and drives off carbon dioxide. A single compound splitting into simpler substances under heat is the definition of thermal decomposition. The balanced equation gives copper(II) oxide as the solid product, \(\mathrm{CuCO_{3}} \rightarrow \mathrm{CuO} + \mathrm{CO_{2}}\); the paper's version writes the solid as Cu, but either way the reaction type is the same.It is not an acid-base reaction, since no acid or base reacts. Chemiluminescence is the emission of light by a chemical reaction, which does not happen here. Photometry is a measuring technique, not a type of reaction.

Q: An element 94A238 forms another element B after one α-particle. The atomic number and the atomic mass of the element B will be :

Element B has atomic number and mass 92 and 234 respectively.An alpha particle is a helium nucleus, two protons and two neutrons, so alpha emission lowers the atomic number by 2 and the mass number by 4:\[ \begin{aligned} Z &= 94 - 2 = 92 \\ A &= 238 - 4 = 234 \end{aligned} \]92 and 236 subtracts only 2 from the mass. 95 and 238 is the result of a beta-minus emission, which raises the atomic number by one and leaves the mass unchanged. 93 and 234 takes the right mass loss but the wrong charge loss.

Q: Which property represents the amount of heat required to raise the temperature of a unit mass of a substance by one degree celsius ?

The property is specific heat.Specific heat (specific heat capacity) is the heat needed to raise the temperature of unit mass of a substance by one degree, in J/(kg K). Water has a very high specific heat, about 4,186 J/(kg K), which is why oceans moderate climate.Heat capacity is the heat needed to raise the temperature of a whole body by one degree; it depends on how much material there is, not on unit mass. Latent heat is absorbed or released during a change of state with no change of temperature. Thermal conductivity measures how readily a material conducts heat, not how much heat it stores.

Q: According to the second law of thermodynamics, in any energy transfer or transformation, the total entropy of a closed system always :

The total entropy always increases.The second law of thermodynamics states that in any spontaneous energy transfer or transformation the entropy of an isolated system increases; some energy is always degraded to low-grade heat. In ecology this is why energy cannot be recycled through a food chain and why only a fraction passes from one trophic level to the next.Strictly, entropy stays constant only in an ideal reversible process, so it never decreases. It does not reach zero, which happens only for a perfect crystal at absolute zero (the third law). 'Negative' is not a possible value of absolute entropy.

The following reaction is an example of CuCO₃ → Cu + CO₂

A.Acid base reaction
B.Chemiluminescence
C.Thermal decomposition
D.Photometry

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: C

The reaction is a thermal decomposition.

Heating copper(II) carbonate breaks it down and drives off carbon dioxide. A single compound splitting into simpler substances under heat is the definition of thermal decomposition. The balanced equation gives copper(II) oxide as the solid product, \(\mathrm{CuCO_{3}} \rightarrow \mathrm{CuO} + \mathrm{CO_{2}}\); the paper's version writes the solid as Cu, but either way the reaction type is the same.

It is not an acid-base reaction, since no acid or base reacts. Chemiluminescence is the emission of light by a chemical reaction, which does not happen here. Photometry is a measuring technique, not a type of reaction.

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An element ₉₄A²³⁸ forms another element B after one α-particle. The atomic number and the atomic mass of the element B will be :

A.92 and 236 respectively
B.95 and 238 respectively
C.92 and 234 respectively
D.93 and 234 respectively

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: C

Element B has atomic number and mass 92 and 234 respectively.

An alpha particle is a helium nucleus, two protons and two neutrons, so alpha emission lowers the atomic number by 2 and the mass number by 4:

\[ \begin{aligned} Z &= 94 - 2 = 92 \\ A &= 238 - 4 = 234 \end{aligned} \]

92 and 236 subtracts only 2 from the mass. 95 and 238 is the result of a beta-minus emission, which raises the atomic number by one and leaves the mass unchanged. 93 and 234 takes the right mass loss but the wrong charge loss.

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Which property represents the amount of heat required to raise the temperature of a unit mass of a substance by one degree celsius ?

A.Latent heat
B.Specific heat
C.Thermal conductivity
D.Heat capacity

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: B

The property is specific heat.

Specific heat (specific heat capacity) is the heat needed to raise the temperature of unit mass of a substance by one degree, in J/(kg K). Water has a very high specific heat, about 4,186 J/(kg K), which is why oceans moderate climate.

Heat capacity is the heat needed to raise the temperature of a whole body by one degree; it depends on how much material there is, not on unit mass. Latent heat is absorbed or released during a change of state with no change of temperature. Thermal conductivity measures how readily a material conducts heat, not how much heat it stores.

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According to the second law of thermodynamics, in any energy transfer or transformation, the total entropy of a closed system always :

A.Increases
B.Decreases
C.Reaches zero
D.Negative

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: A

The total entropy always increases.

The second law of thermodynamics states that in any spontaneous energy transfer or transformation the entropy of an isolated system increases; some energy is always degraded to low-grade heat. In ecology this is why energy cannot be recycled through a food chain and why only a fraction passes from one trophic level to the next.

Strictly, entropy stays constant only in an ideal reversible process, so it never decreases. It does not reach zero, which happens only for a perfect crystal at absolute zero (the third law). 'Negative' is not a possible value of absolute entropy.

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Which one of the following radionuclides has the lowest half life period ?

A.\(\mathrm{C}^{14}\)
B.\(\mathrm{Sr}^{90}\)
C.\(\mathrm{I}^{131}\)
D.\(\mathrm{Cs}^{137}\)

Exam Year(s)

UGC NET - 2012,

Answer: C

The half life of iodine-131 is about 8 days, whereas carbon-14 has about 5,730 years, strontium-90 about 29 years and caesium-137 about 30 years. So iodine-131 has by far the shortest half life of the four. It is a major short-term radiological hazard after a reactor accident because it collects in the thyroid, but it decays away within weeks, while the other three persist for decades or millennia.

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