Tag: chemistry

Quizzes (490) Questions (9892)

Questions Related to chemistry

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

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

  1. $ZnO$
  2. $Al _2O _3$
  3. $CuO$
  4. $CaO$
Reveal answer Fill a bubble to check yourself
B,D Correct answer
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 .

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

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:

  1. sorption

  2. desorption

  3. physisorption

  4. chemisorption
Reveal answer Fill a bubble to check yourself
B Correct answer
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. 

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

The lowering of activation energy by catalyst is due to

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

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

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

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
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.)

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

In a chemical reaction, the solid catalyst function as:

  1. Adsorbent

  2. Adsorbate

  3. Micelle

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In heterogeneous catalysis where a solid catalyst is used, reactant molecules in gaseous or liquid phase accumulate on the surface of the solid catalyst. This surface phenomenon is known as adsorption.

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

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

  1. desorption

  2. absorbation

  3. adsorbation

  4. none
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

The name catalysis was given by: 

  1. Rutherford

  2. Langmuir

  3. Graham

  4. Berzelius
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Adsorption increases the reaction rate by concentrating reactant molecules on the surface of the catalyst, which increases the frequency of effective collisions. This is the fundamental principle of surface catalysis.

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

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

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
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.