17.Oxygen gas can be prepared by heating potassium chlorate according to the following equation: 2KClO3(s)2KCl(s) + 3O2(g)

The product gas, O2, is collected over water at a temperature of 25 °C and a pressure of 755 mm Hg. If the wet O2 gas formed occupies a volume of 6.22 L, the number of grams of O2 formed is
g. The vapor pressure of water is 23.8 mm Hg at 25 °C.

Mass of O₂ formed = 7.84 g

Given

Reaction

2KClO₃(s) ⇒2KCl(s) + 3O₂(g)

P water = 23.8 mmHg

P tot = 755 mmHg

V = 6.22 L

T = 25 + 273 = 298 K

Required

mass of O₂

Solution

P tot = P O₂ + P water

P O₂ = P tot - P water

P O₂ = 755 - 23.8

P O₂ = 731.2mmHg = 0.962 atm

Ideal gas law :

n = PV/RT

n = 0.962 x 6.22 / 0.082 x 298

n = 0.245

= mol x MW

= 0.245 x 32

= 7.84 g

describe matter a earth

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

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.