Tag: chemistry

Questions Related to chemistry

The reactions $PCl 5 (g)  \rightleftharpoons  PCl _3(g) + Cl _2 (g) $ and $COCl _2 (g)  \rightleftharpoons  CO(g) + Cl _2(g)$ are simultaneously in equilibrium in an equilibrium box at constant volume. A few moles of CO(g) are later introduced into the vessel. After some time, the new equilibrium concentration of_______.

chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. PCl$ _5$ will remain unchanged

  2. Cl$ _2$ will be greater

  3. PCl$ _5$ will become less

  4. PCl$ _5$ will become greater

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Correct Option: C
Explanation:

If CO is added 2$^{nd}$ equilibrium will proceed in the backward direction and concentration of Cl$ _2$ will decrease. This Cl$ _2$ will be further formed by the decomposition of PCl$ _5$.

If two gases $AB _2$ and $B _2C$ are mixed the following equilibria are readily established
$AB _2(g) + B _2 C(g)  \rightarrow AB _3(g) + BC(g)$
$BC(g) + B _2 C(g)  \rightarrow B _3 C _2 (g)$
If the reaction is started only with $AB _2$ with $B _2C$, then which of the following is necessarily true at equilibrium:

chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. $[AB _3] _{eq} = [BC] _{eq}$

  2. $[AB _2] _{eq} = [B _2C] _{eq}$

  3. $[AB _3] _{eq} > [B _3C _2] _{eq}$

  4. $[AB _3] _{eq} > [BC] _{eq}$

Show answer
Correct Option: C,D
Explanation:

Let reactions is started with a mole of $AB _2$ and b mole of $B _2C$
$\Rightarrow      AB _2 (g) + B _2C(g)  \rightarrow AB _3(g) + BC(g)$
                    a                 b               0               0
                  a - x           b - x - y        x              x - y
$BC(g) + B _2C(g)   \rightarrow B _2C _2 (g)$
    x - y            b - x - y        y                 As  x > y
Clearly $[AB _3] _{eq} > [B _3 C _2] _{eq} $ and  $[AB _3] _{eq}  >  [BC] _{eq}$

When the equilibrium is attained, the concentration of each of the reactants and products becomes equal.
chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. True

  2. False

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Correct Option: B
Explanation:

When the equilibrium is attained, the concentration of each of the reactants and products may or may not become equal.  It may happen that the concentrations of products are higher than the concentrations of the reactants. Or, it may happen that the concentrations of the reactants are higher than the concentrations of the products.

At 373 K,a gaseous reaction $A\rightarrow 2B+C$ is found to be of first order.Starting with pure A,the total pressure at the end of 10 min was 176 mm of Hg and after a long time when A was completely dissociated,it was 270 mm of Hg.The pressure of A at the end of  10 minutes was:

chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. 94 mm of Hg

  2. 47 mm of Hg

  3. 43 mm of Hg

  4. 90 mm of Hg

Show answer
Correct Option: B
Explanation:

                    $A \to 2B + C$

$at\,t = 0$   $x$       $0$    $0$

$at\,t = 10$    $x-y$           $2y$    $y$  

 $total=x-y+2y+y$

        $=x+2y=176\,mm$-------$(i)$

$at\,{t={100}}$   $0$       $2x$    $x$

$total=2x+x=270\,mm$

$ \Rightarrow 3x = 270$
$ \Rightarrow x = 90\,mm\,\,of\,Hg$

put the value of $A$ in $e{q^n}\,(i),$ we get
   $x+2y=176$
$ \Rightarrow 90 + 2y = 176$
$ \Rightarrow  2y = 86$
$ \Rightarrow y=43\,\,\,mm\,\,of\,Hg$

At the end of $10$ min pessure of $A$ is  $x-y=90-43=47\,mm\,of\,Hg$

Option B is correct.

If you have a solution in equilibrium containing $Cl^-$ ions and you added $NaCl$ to the solution, what is going to happen?

chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. The reaction will shift to the left to compensate for the increased concentration of $Cl^-$ ions

  2. The reaction will become unbalanced and stay unbalanced

  3. Le Chatelier's principle says that nothing will happen

  4. More $Na^+$ ions will be made so that concentrations of $Na^+$ and $Cl^-$ even out

  5. Equilibrium will be restored

Show answer
Correct Option: A
Explanation:

If you have a solution in equilibrium containing $Cl^-$ ions and you added $NaCl$ to the solution, the reaction will shift to the left to compensate for the increased concentration of $Cl^-$ ions. This is in accordance with the  Le Chatelier's Principle .
The Le Chatelier's Principle states that any change in a substance on one side of the equation, either in concentration, temperature, pressure or volume, results in an equilibrium shift to oppose the change until a new equilibrium is reached.

Which is the following are true about the chemical equilibrium?

chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. The chemical equilibrium is a state in which the rate of the forward reaction is equal to the rate of the reverse reaction.

  2. The chemical equilibrium takes at least 10 hours to be established.

  3. The chemical equilibrium is a state in which the rate of the forward reaction is not equal to the rate of the reverse reaction.

  4. The chemical equilibrium can only occur at temperatures above room temperature.

  5. None of these answers are correct

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Correct Option: A
Explanation:

The following is true about the chemical equilibrium.
The chemical equilibrium is a state in which the rate of the forward reaction is equal to the rate of the reverse reaction. A chemical equilibrium is a state of balance in a reaction where the forward and reverse reaction speed is equal and the concentrations of the products and reactants remain unchanged.

Identify the common property for a chemical reaction at dynamic equilibrium.

chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. The measurable properties like concentration, density, colour, pressure etc remain constant at constant temperature

  2. The forward and backward reactions take place with the same rate

  3. It can be achieved from both directions

  4. All of the above

Show answer
Correct Option: D
Explanation:

At dynamic equilibrium, the reaction rate of the forward reaction is equal to the reaction rate of the backward reaction. A dynamic equilibrium exists once a reversible reaction ceases to change its ratio of reactants/products, but substances move between the chemicals at an equal rate, meaning there is no net change. It is a particular example of a system in a steady state. Equilibrium is the state of equal, opposite rates, not equal concentrations. The measurable properties like concentration, density, color, pressure etc remain constant at constant temperature.

When equilibrium is attained, the concentration of each of the reactants and products become equal.

chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. True

  2. False

  3. Ambiguous

  4. None of these

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Correct Option: A
Explanation:

Equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time.Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but equal. Thus, there are no net changes in the concentrations of the reactant(s) and product(s).

In reversible reactions concentration of:

chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. reactants decreases with time at equilibrium

  2. products increases with time at equilibrium

  3. reactants decreases and then increases with time at equilibrium

  4. reactants and products are constant at equilibrium

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Correct Option: D
Explanation:

In reversible reactions, as equation the rates of forward and backward reactions are same so the concentrations of reactants and products are constant at equilibrium.

Which of the following factors are equal in a reversible chemical reaction at equilibrium?

chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. The number of moles of the reactants and products

  2. The potential energies of the reactants and products

  3. The activation energies of the forward and reverse reactions

  4. The rates of reaction for the forward and reverse reactions

  5. The concentrations of the reactants and products.

Show answer
Correct Option: D
Explanation:

The rates of reaction for the forward and reverse reactions are equal in a reversible chemical reaction at equilibrium. When the concentrations of reactants and products have become constant, a reaction is said to have reached a point of equilibrium. The consistency of measurable properties such as concentration, color, pressure and density can show a state of equilibrium. The rates of the two opposing reactions have become equal. The amount of products and reactants produced are consistent, and there is no net change.