Convert 0.123kg sio2 to moles. use three significant figures

2.05 moles of SiO₂

Explanation:

1- The molar mass of the compound must be calculated. To do this, with the help of a periodic table the atomic weights of the elements of the compound are sought and the sum of them is performed:

mSiO₂= mSi + 2 x mO = 28.09 g + 2 x 15.99 g = 60.07 g / mol

2- Once the molar mass is obtained, you can calculate the number of moles that represent the amount of SiO₂ in the statement. Since the data is in units of kilograms, and the molecular mass that has been calculated is in grams, a unit conversion of some of the two data must be performed, to have them in the same unit. All data will be passed to grams.

So:

1 kg 1000 g

0.123 kg X = 123 g

Calculation: (0.123 kg x 1000g) / 1 kg = 123 g of sample

3- Now the mass of SiO₂ can be converted to moles:

60.07 g SiO₂ 1 mol

123 g SiO₂ X = 2.0476 mol

Calculation: (123 g x 1 mol) / 60.07 g = 2.0476 mol ≅ 2.05 mol

As the statement says that we use three significant figures, only three figures of the calculated result are left and according to the fourth figure obtained that is a 7, we round the last significant figure by adding a unit.

As a result, 0.123 kg of SiO₂ equivalent to 2.05 moles.

answer: the value of enthalpy change will be -152.80 kj.

solution:

pressure = 1atm , temperature = = 298 k

given that pressure and temperature are same in both gases , the number of moles of both gases can be determined by the ideal gas equation.

according to reaction 3 moles no are reacting with 1 mol of ,then 0.49 mol of no will react with moles of ozone that is 0.16 moles of ozone. since, no is limiting reagent and is an excessive reagent.

enthalpy change for the reaction between the given volumes of the gases is :

im not exactly sure but i think its b!