Stoichiometry (8A. S, 8B. R, 8G. S, 8H. S]:Question 4
What is the mass of 1.204 x1024 particles of Li2O?

                    59.76 grams of Li₂O

Explanation:

To solve this problem we will first calculate the moles of Li₂O.                       One mole of given substance always contains 6.022 × 10²³ particles  which can be atoms, ions, molecules or formula units. This number is also called as Avogadro's Number.

The relation between Moles, Number of Particles and Avogadro's Number is given as,

                         Number of Moles  =  Number of Particles ÷ 6.022 × 10²³

Putting values,

                         Number of Moles  =  1.204 × 10²⁴ Particles ÷ 6.022 × 10²³

                         Number of Moles  =  2.0 Moles

Secondly, we will convert calculated moles to mass using following relationship.

                         Moles  =  Mass  /  M.Mass

Or,

                         Mass  =  Moles  ×  M.Mass

Putting values,

                         Mass  =  2.0 mol × 29.88 g/mol

                         Mass  =  59.76 grams of Li₂O

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"