The rate constant for a first order reac | Class 12 Chemistry Chapter Chemical Kinetics, Chemical Kinetics NCERT Solutions

Question:

Calculate the molecular mass of the following:
(i) H2O
(ii) CO2
(iii) CH4

Answer:

Molecules are made up of atoms & are  quite small, therefore the actual mass of a molecule cannot be detrmined.It is expressed as the relative mass.C-12 isotope is used to express the relative molecular masses of substances.Thus  molecular mass of a substance may be defined as: the average relative mass of its molecule as compared to the mass of carbon atom taken as 12 amu.

(i) H2O:

The molecular mass of water, H2O

= (2 × Atomic mass of hydrogen) + (1 × Atomic mass of oxygen)

= [2(1.0084) + 1(16.00 u)]

= 2.016 u + 16.00 u

= 18.016

= 18.02 u

(ii) CO2:

The molecular mass of carbon dioxide, CO2

= (1 × Atomic mass of carbon) + (2 × Atomic mass of oxygen)

= [1(12.011 u) + 2 (16.00 u)]

= 12.011 u + 32.00 u

= 44.01 u

(iii) CH4:

The molecular mass of methane, CH4

= (1 × Atomic mass of carbon) + (4 × Atomic mass of hydrogen)

= [1(12.011 u) + 4 (1.008 u)]

= 12.011 u + 4.032 u

= 16.043 u


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Comments

  • Aqeel Ahmad
  • 2019-08-01 20:20:17

My dear the value of log 16 is 1.2(approx). Hope it helps you.


  • Aynal Hoque
  • 2018-10-23 11:31:50

It's very simple...1st find Half life then follow the following process.. 1 to 1/2 to 1/4 to 1/8 to 1/6 Here clearly seen that 4 half life required so multiplied the the half life with 4 ...you will get correct answer..


  • Aman kumar
  • 2018-08-16 20:01:37

Plz send me the clear solution..plzz


  • Aman kumar
  • 2018-08-16 20:01:09

I can't understand how log16 is changed in simple form


Comment(s) on this Question

Welcome to the NCERT Solutions for Class 12 Chemistry - Chapter . This page offers a step-by-step solution to the specific question from Excercise 2 , Question 16: The rate constant for a first order reaction is 60 s-1. How much time will it take to reduce the ini....