True!
For example:
The atomic mass of carbon is 12.011 (i think) and the weight of carbon is 12. But with C13 and C14 being a little higher, it makes the average higher. Random fact: C14 is used for carbon dating.
Answer:
Units of a = 
Units of b = 
Explanation:
The Van der Waal's equation is:-

Where,
P is the pressure
V is the volume
n is the number of moles
T is the temperature
R is Gas constant having value
a and b are van der Waal's constant
If pressure is taken in atm and volume in L. So,
represents the pressure correction term. Then,
Units of a = 
represents the volume correction term. Then,
Units of b = 
Answer: 72 grams of
are needed to completely burn 19.7 g 
Explanation:
According to avogadro's law, 1 mole of every substance weighs equal to molecular mass and contains avogadro's number
of particles.
To calculate the number of moles, we use the equation:

Putting in the values we get:


According to stoichiometry:
1 mole of
requires 5 moles of oxygen
0.45 moles of
require=
moles of oxygen
Mass of 
72 grams of
are needed to completely burn 19.7 g 
<span>(1) The atom absorbs energy, and one or more electrons move to a higher electron shell.</span>