Magnesium reacts with iron(III) chloride to form magnesium chloride (which can be used in fireproofing wood and in disinfectants) and iron. A mixture of 43.5 g Mg and 247 g iron(III) chloride is allowed to react. What is the limiting reactant and what is the mass, in grams, of the excess reactant remains

Mg is the limiting reactant.

52.9 g of FeCl₃, remains after the reaction is complete.

Explanation:

First of all, we state the reaction's equation:

3Mg (s) + 2FeCl₃ (aq) → 2Fe (s) + 3MgCl₂ (s)

We determine the mol of each reactant:

43.5 g . 1mol / 24.3g = 1.79 mol of Mg

247 g . 1mol/ 162.2g = 1.52 mol of Iron (III) chloride.

Ratio is 2:3. 2 mol of chloride need 3 moles of Mg to react,

Then 1.52 moles will react with (1.52 . 3) /2 = 2.29 moles

We have 1.79 moles of Mg and we need 2.29, so the limiting reactant is the Mg.

We confirm the chlorine as the excess reactant:

3 moles of Mg need 2 moles of FeCl₃ to react:

1.79 moles of Mg will react to (1.79 . 2) /3  = 1.19 moles of FeCl₃

We have 1.52 moles of FeCl₃ and we only need 1.19, so it is ok, we said that the FeCl₃ is the excess.

After the reaction goes complete, (1.52 - 1.19) moles of FeCl₃ remains.

1.52 - 1.19 = 0.33 moles. We convert them to mass:

0.33 mol . 162.2g /1mol = 52.9 g

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.