Tag: chemistry

Questions Related to chemistry

Which of the following oxides cannot be reduced to metal by carbon?

chemistry production of metals extraction of metal from concentrated ore basics of metallurgy extraction of metals from ore

  1. $ZnO$

  2. $Al _2O _3$

  3. $CuO$

  4. $CaO$

Show answer
Correct Option: B,D
Explanation:

Generally carbon is more reactive than $Zn$ and $Cu$. Hence, $ZnO$ and $CuO$ can be reduced by carbon leading to the formation of corresponding metals,  but carbon is less reactive than $Ca$ and $Al$, so $CaO$ and $Al _2O _3$ can not be reduced by carbon .

After the reaction is over between adsorbed reactants, it is important to create space for the other reactant molecules to approach the surface and react. The process responsible for this is known as:

chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

  1. sorption

  2. desorption

  3. physisorption

  4. chemisorption

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Correct Option: B
Explanation:

After the reaction is over between adsorbed reactants, the process of desorption is important to remove products and further create space for the other reactant molecules to approach the surface and react. 

The addition of 1% alcohol to chloroform acts as a

chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

  1. positive catalyst

  2. negative catalyst

  3. autocatalyst

  4. none of these

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Correct Option: B
Explanation:

Addition of 1% alcohol to chloroform acts as negative catalyst because it decreases the rate of decomposition of CHCl$ _3$.

The lowering of activation energy by catalyst is due to

chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

  1. formation of adsorbed activated complex and to provide new pathway to reaction

  2. adsorption is always exothermic

  3. the adsorbed activated complex possesses lower energy level than simple activated complex

  4. all the above

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Correct Option: A
Explanation:

The lowering of activation energy by catalyst is due to formation of adsorbed activated complex and to provide new pathway to reaction.

$KClO _3$ on heating decomposes  into $KCl$ and $O _2$. If some $MnO _2$ is added, the reaction goes much faster because :

chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

  1. $MnO _2$ decomposes to give oxygen

  2. $MnO _2$ provides heat by reacting

  3. better contact is provided by $MnO _2$

  4. $MnO _2$ acts as a catalyst

Show answer
Correct Option: D
Explanation:

The reaction is as follows:
$2KClO _3\xrightarrow {heat} 2KCl+3O _2$
In this reaction, if $MnO _2$ is used, then the reaction become faster due to catalytic activities of $MnO _2$.

(Catalyst is a substance which lowers activation energy of reaction because it provides alternate pathway for reaction. Also, it increases the rate of backward and forward reaction with same extent. Due to this lower activation energy, equilibrium is attained faster but it doesnot change the overall enthalpy of the reaction.)

In a chemical reaction, the solid catalyst function as:

chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

  1. Adsorbent

  2. Adsorbate

  3. Micelle

  4. None of the above

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Correct Option: B

Removal of adsorbate from the surface of adsorbent is called _____.

chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

  1. desorption

  2. absorbation

  3. adsorbation

  4. none

Show answer
Correct Option: A
Explanation:

Removal of adsorbate from the surface of adsorbent is called desorption.
It is the reverse of adsorption. 

For example, when hydrogen gas is adsorbed on the surface of Pt and the temperature is raised or pressure is lowered, some of the hydrogen gas escapes from the surface of Pt. This is known as desorption.

The name catalysis was given by: 

chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

  1. Rutherford

  2. Langmuir

  3. Graham

  4. Berzelius

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Correct Option: D
Explanation:

The word catalysis was first used by Berzelius in 1836 to describe a number of experimental reactions. Catalysis is defined as a phenomenon in which the presence of a foreign compound in a reaction can accelerate its rate without being used  in that reaction. These foreign substances are called as a catalyst.

According to adsorption theory of catalysis, the reaction rate increases, because:

chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

  1. Adsorption produces heat which increases the rate of reaction

  2. In the process of adsorption, the kinetic energy of the molecules increases

  3. The concentration of reactants at the active centres becomes high due to adsorption

  4. The activation energy of the reaction becomes high due to adsorption

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Correct Option: C

In which of the following processes, a catalyst is not used? 

chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

  1. Haber's process and Deacon's process

  2. Deacon's process and Solvay process

  3. Solvay process and Lead chamber process

  4. None of these can proceed without catalyst

Show answer
Correct Option: D
Explanation:

Haber's process catalyst is finely divided iron

Deacon's process catalyst is copper chloride

Solvay process catalyst is ammonia-soda

Lead chamber process catalyst is platimnum.

So in the all above process is catalyst is used.