Calculate the heat evolved kJ for the reaction of 1.00 g of elemental sulfur.
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Answer:
Explanation:
To convert from moles to grams, the molar mass must be used.
1. Find Molar Mass
The compound is iron (III) chloride: FeCl₃
First, find the molar masses of the individual elements in the compound: iron (Fe) and chlorine (Cl).
- Fe: 55.84 g/mol
- Cl: 35.45 g/mol
There are 3 atoms of chlorine, denoted by the subscript after Cl. Multiply the molar mass of chlorine by 3 and add iron's molar mass.
- FeCl₃: 3(35.45 g/mol)+(55.84 g/mol)=162.19 g/mol
This number tells us the grams of FeCl₃ in 1 mole.
2. Calculate Moles
Use the number as a ratio.
Multiply by the given number of grams, 345.0.
Flip the fraction so the grams of FeCl₃ will cancel.
Divide.
3. Round
The original measurement of grams, 345.0, has 4 significant figures. We must round our answer to 4 sig figs.
For the answer we calculated, that is the thousandth place.
The 1 in the ten thousandth place tells us to leave the 7 in the thousandth place.
There are about <u>2.127 mole</u>s of iron (III) chloride in 345.0 grams.