The integrated circuits in your cell phone and computer are made from the semiconductor silicon. The silicon is obtained from a really inexpensive starting material, sand, which is primarily SiO2. One step in the purification of silicon is to separate it from solid impurities by forming the gas silicon tetrachloride. Given the following reactions, which are performed one at a time, what is the overall enthalpy change in converting 1.00 mol of silicon dioxide into pure silicon? Reaction ΔH° (kJ) SiO2(s) + 2C(s) → Si(impure s) + 2CO(g) +690 Si(impure s) + 2Cl2(g) → SiCl4(g) −657 SiCl4(g) + 2Mg(s) → 2MgCl2(s) + Si(s) −625 Select one: a. −592 kJ b. −1,972 kJ c. +592 kJ d. −625 kJ e. +1,972 kJ
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
The integrated circuits in your cell phone and computer are made from the semiconductor silicon. The silicon is obtained from a really inexpensive starting material, sand, which is primarily SiO2. One step in the purification of silicon is to separate it from solid impurities by forming the gas silicon tetrachloride. Given the following reactions, which are performed one at a time, what is the overall enthalpy change in converting 1.00 mol of silicon dioxide into pure silicon?
|
Reaction
|
ΔH° (kJ)
|
| SiO2(s) + 2C(s) → Si(impure s) + 2CO(g) |
+690
|
| Si(impure s) + 2Cl2(g) → SiCl4(g) |
−657
|
| SiCl4(g) + 2Mg(s) → 2MgCl2(s) + Si(s) |
−625
|
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