Tag: chemistry

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Questions Related to chemistry

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

The rate constant for the reaction is $2 10^{-4} s^{-1}.$ The reaction is :

  1. First order

  2. Second order

  3. Third order

  4. Zero order
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The unit of the rate constant is s^-1. This unit is characteristic of a first-order reaction, where the rate constant k has dimensions of time^-1.

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

For a second-order reaction of the type rate=$k[A]^2$ the plot of $\dfrac{1}{[A] _1}$ versus t is linear with a: 

  1. positive slope and zero intercept

  2. positive slope and non-zero intercept

  3. negative slope and zero intercept

  4. negative slope and non-zero intercept
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given that for a second order reaction

$Rate= K[A]^2$

We know that rate of the reaction is decrease in the concentration of the reactant with respect to time.

$Rate= \cfrac {-d[A]}{dt}$
$\Rightarrow$ $\cfrac {-d[A]}{dt}=K[A]^2$
$\Rightarrow \cfrac {-d[A]}{[A]^2}=+Kdt$

Integrating both sides we have:-
$\Rightarrow -\int \cfrac {d[A]}{[A]^2}=+\int Kdt$
$\Rightarrow - \left[\cfrac {-1}{[A]}\right]=+Kt+C$
$\Rightarrow Kt+C= \cfrac {1}{[A]}$      $- (i)$

Now, from the equation $(i)$ we can see that graph of $\cfrac {1}{[A]}$ $V/s$ $t$ has a positive slope $K$ and non-zero intercept $C$.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

22.4 litres of a gas at STP weighs 16 g. Identify the gas.

  1. Methane

  2. Carbon monoxide

  3. Ethane

  4. Oxygen
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

At STP,  1 mole of gas occupies $22.4l$.

Given gas occupies $22.4l$ at STP and has weight 16 g.
So molecular weight of gas is 16. 
Thus Ans: Methane (Mol. weight of methane is 16)

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

All gases have the same number of moles in the same volume at constant temperature and pressure.

  1. Boyle's Law

  2. Charles's Law

  3. Avogadro's Principle

  4. Ideal Gas Law
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to the Avogadro's principal, every gas have the same number of moles in the same volume at constant temperature and pressure.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

What is the volume of $3.0\times {10}^{20}$ molecules of $HCl (g)$?

  1. $11.2L$
  2. $0.0224L$
  3. $0.0112L$
  4. $22.4L$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$1 \space Mole$ of gas at STP occupy $22.4 \space Litres$ of gas

As, $1 \space Mole = 6.02 \times 10^{23}$ molecules $\Rightarrow 22.4 Litres$ 
$3.0 \times 10^{20}$ molecules $\Rightarrow (X)$ 
$\Rightarrow X = \dfrac{22.4 \times 3 \times 10^{20}}{6.02 \times 10^{23}} = 0.0112\space L$

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

All gases have the same number of moles in the same volume at constant T and P is stated by :

  1. Boyle's law

  2. Charle's law

  3. Avogardro's law

  4. ideal gas law

  5. Dalton's law
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Avogadro's law states that, "equal volumes of all gases, at the same temperature and pressure, have the same number of molecules". For a given mass of an ideal gas, the volume and amount (moles) of the gas are directly proportional if the temperature and pressure are constant.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

Which statement is linked with the idea that two identical containers filled with different gases will contain the same number of particles?

  1. Mosely

  2. Avagadro

  3. Dalton

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

Avagadro stated that when two identical containers are filled with different gases at same pressure and temperature, they contain same number of particles.

So, the statement is linked with Avagadro.

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

What is the volume occupied by 17.75 g of $Cl _2$ at STP?

  1. $5.6l$
  2. $22.4l$
  3. $11.2l$
  4. $2.8l$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In order to solve this problem, we would use the ideal gas law formula PV = nRT 

at STP standard temp and pressure is 1 atm and 273k

we have 

P = 1atm, n = $\dfrac{17.75}{70.90}$ mole = 0.250, R = $0.0821$ $atm*L/mol*K$ , T=$273K$

V = $\dfrac {nRT}{P}$

= $0.250\times 0.0821\times 273$

= $5.6L$

answer is A


Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

Which term describes the mass of $6.022\times { 10 }^{ 23 }$ representative particles?

  1. Molar mass

  2. Avogadro's number

  3. Empirical formula

  4. Molecular formula
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Molar mass of a compound describes the total mass of $6.023 \times 10^{23}$ atoms or particles of the compound.

Ex: Molar mass of $H _2 = 2\space g$

Multiple choice chemistry quantitative chemistry avogadro hypothesis avogadro's law avogadro law

A sample of ammonia has a mass of $51.1g$. How many molecules are in this sample?

  1. $1.8\times {10}^{23}$ molecules
  2. $3.6\times {10}^{23}$ molecules
  3. $9.1\times {10}^{23}$ molecules
  4. $1.8\times {10}^{24}$ molecules
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
given mass of ammonia is 51.1g
in this number of moles =  $\dfrac{51.1}{17.031}$ = 18
Now in a mole, there are Na molecules, this is known $6.023\times 10^{23}$ 
since 1 mol = $6.023\times 10^{23}$ 

thus,

18 mol = $18\times 6.023\times 10^{23}$  = $1.8\times 10^{24}$