Tag: chemistry

Questions Related to chemistry

Consider the chemical reaction:
$N _2(g)+3H _2(g)\rightarrow 2NH _3(g)$


The rate of this reaction can be expressed; in terms of time and of concentration of $N _2(g), H _2(g)$ $NH _3(g)$. Identify the correct relationship amongst the rate expressions.

chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

  1. Rate $=-\dfrac{d[N _2]}{dt}=-\dfrac{1}{3}\dfrac{d[H _2]}{dt}=+\dfrac{1}{2}\dfrac{d[NH _3]}{dt}$

  2. Rate $=-\dfrac{d[N _2]}{dt}=-\dfrac{3d[H _2]}{dt}=\dfrac{2d[NH _3]}{dt}$

  3. Rate $=-\dfrac{d[N _2]}{dt}=-\dfrac{1}{3}\dfrac{d[H _2]}{dt}=\dfrac{d[NH _3]}{dt}$

  4. Rate $=-\dfrac{d[N _2]}{dt}=\dfrac{d[H _2]}{dt}=\dfrac{d[NH _3]}{dt}$

Show answer
Correct Option: A
Explanation:

As the reaction proceed, the concentration of the reactant decrease and that of the product increases.
Thus, the rate of the reaction of the reactant and product can be given as follow:
$Rate =-\cfrac{d}{dt}[N _2]=-\cfrac{1}{3}\cfrac{d}{dt}[H _2]=+\cfrac{1}{2}\cfrac{d}{dt}[NH _3]$

Rate of formation of $SO _3$ in the following reaction $2SO _2+O _2\rightarrow 2SO _3$ is $100g$ $min^{-1}$. 


Then the rate of disappearance of $O _2$ is:

chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

  1. $50g$ $min^{-1}$

  2. $40g$ $min^{-1}$

  3. $200g$ $min^{-1}$

  4. $20g$ $min^{-1}$

Show answer
Correct Option: A
Explanation:

$2{ SO } _{ 2 }+{ O } _{ 2 }\rightarrow 2{ SO } _{ 3 }$


rate $=\dfrac { 1 }{ 2 } \dfrac { \left[ { \triangle SO } _{ 2 } \right]  }{ \triangle t } =\dfrac { \triangle \left[ { O } _{ 2 } \right]  }{ \triangle t } =\dfrac { 1 }{ 2 } \dfrac { \triangle \left[ { SO } _{ 3 } \right]  }{ \triangle t } $

rate of formation of ${ SO } _{ 3 }=$ rate of disappearance of ${ O } _{ 2 }$

$\dfrac { 1 }{ 2 } \dfrac { \triangle \left[ { SO } _{ 3 } \right]  }{ \triangle t } =-\dfrac { \triangle \left[ { O } _{ 2 } \right]  }{ \triangle t } $

$-\dfrac { \triangle w _{{ O } _{ 2 }}   }{ \triangle t }=\dfrac { 1 }{ 2 } \times \dfrac{100}{80}\times 32g{ min }^{ -1 }=20g{ min }^{ -1 }$

So, the correct option is $D$

If concentration of reactants is increased by a factor x then the rate constant k becomes:

chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

  1. $\ln{\frac{k}{x}}$

  2. $\frac{k}{x}$

  3. $k+x$

  4. $k$

Show answer
Correct Option: D
Explanation:

Rate Constant doesn't depend on the concentration of the reactants.

So, If the conc of reactants is increased by a factor x, then the rate constant k becomes k.

An aqueous solution of $CH _3COOH$ has a pH = $3$ and acid dissociation constant of $CH _3COOH$ is $10^{-5}$. What will be the concentration of acid taken initially?

chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

  1. $0.1$M

  2. $0.11$M

  3. $0.09$M

  4. $0.101$M

Show answer
Correct Option: A
Explanation:

${H}^{+} = \sqrt{{K} _{a} \times {C}}$


${10}^{-6} = {10}^{-5} \times {C}$

${C} = 0.1\space M$

For the non-equilibrium process, $A + B \rightarrow Products$, the rate is first order with respect to $A$ and second-order with respect to $B$. If $1.0$ mole each of $A$ and $B$ are introduced into a 1-litre vessel and the initial rate was $1.0 \times 10^{-2}$ mol/litre-sec. The rate (in mol $litre^{-1} sec^{-1}$) when half of the reactants have been used:

chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

  1. $1.2 \times 10^{-3}$

  2. $1.2 \times 10^{-2}$

  3. $2.5 \times 10^{-4}$

  4. none of these

Show answer
Correct Option: A
Explanation:

$rate = k[A]{[B]}^{2}$


Initially 1 mol each of A and B are present and the rate was $1 \times {10}^{-2}\space mol/lit-sec$

When Half of the Reactants are used, the rate becomes $\dfrac{1}{2} \times {[\dfrac{1}{2}]}^{2} \times {10}^{-2}$ = $1.2 \times {10}^{-3}$

 Time  0  5min  10min  15min
 [A]  20mol  18mol  16mol  16 mol

For the reaction $A\longrightarrow Products$; $\frac { -d[A] }{ dt } =k$ and at different time interval, IAI values are given. At $20$ minute, rate will be :

chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

  1. $12 mol /min$

  2. $10 mol/min$

  3. $8 mol/min$

  4. $0.4 mol/min$

Show answer
Correct Option: D
Explanation:

The concentration decreases linearly with time

Hence moles of A at $20 min$
$=12$
Therefore, $k=\dfrac{-d[A]}{dt}$
$=-\dfrac{12-14}{20-15}$
$=0.4\ mol/min$

$H _2 + l _2 \rightarrow 2 Hl$ (An elementary reaction)
If the volume of the container containing the gaseous mixture is increased to two times, then final rate of the reaction

chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

  1. Become four time

  2. Become $\dfrac{1}{4} th$ of the original rate

  3. Become $2$ times

  4. Become $\dfrac{1}{2}$ of the original rate

Show answer
Correct Option: A

Assuming an element reaction $H _2O _2+ 3I^-+ 2H^+\to 2H _2O+ I _3^-.$ The effect on the rate of this reaction brought about by doubling the concentration of $I^-$ without changing the order?

chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

  1. The rate would increases by a factor of $3$

  2. The rate would increase by a factor of $8$

  3. The rate would decrease by a factor of $1/3$

  4. The rate would increase by a factor of $9$

Show answer
Correct Option: B

Statement 1: The temperature of a substance always increases as heat energy is added to the system.
Statement 2: The average kinetic energy of the particles in the system increases with an increase in temperature.

chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

  1. Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1

  2. Both the Statement 1 and Statement 2 are correct and Statement 2 is NOT the correct explanation of Statement 1.

  3. Statement 1 is correct but Statement 2 is not correct.

  4. Statement 1 is not correct but Statement 2 is correct.

  5. Both the Statement 1 and Statement 2 are not correct.

Show answer
Correct Option: A
Explanation:

Energy can neither be created nor be destroyed. It is only converted in one form or the other. Addition of heat energy increases the kinetic energy which is dependent on absolute temperature.

$\therefore $ Temperature also increases when heat energy is added.
Hence, Statement 1 and statement 2 are correct and statement 2 is the correct explanation of statement 1.

Instanteneous rate of reaction can be found be :

chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

  1. slope of a rate of reaction vs time

  2. slope of a concentration vs time graph

  3. taking any two points on the graph

  4. both $B$ and $C$

Show answer
Correct Option: B
Explanation:

We determine an instantaneous rate at time t:

  1. by calculating the negative of the slope of the curve of concentration of a reactant versus time at time t.
  2. by calculating the slope of the curve of concentration of a product versus time at time t.