Consider the formation reaction of SiF4 : SiF4 (g) + 2 H2O (l) SiO2 (s) + 4 HF (
ID: 1029436 • Letter: C
Question
Consider the formation reaction of SiF4 :
SiF4 (g) + 2 H2O (l) SiO2 (s) + 4 HF (g) Kc = 328.8 @ 25°C Kc = 46.3 @ 50°C
1) If pressure of SiF4 is decreased:
What happens to the concentration of SiF4, H2O, SiO2, and HF? Is energy absorbed, produced, not changed, or is not enough information provided?
2) If HF is added:
What happens to the concentration of SiF4, H2O, SiO2, and HF? Is energy absorbed, produced, not changed, or is not enough information provided?
3) if the amount of SiO2 is increased:
What happens to the concentration of SiF4, H2O, SiO2, and HF? Is energy absorbed, produced, not changed, or is not enough information provided?
4) if the energy of the reaction is increased:
What happens to the concentration of SiF4, H2O, SiO2, and HF? Is energy absorbed, produced, not changed, or is not enough information provided?
5) If volume is doubled:
What happens to the concentration of SiF4, H2O, SiO2, and HF? Is energy absorbed, produced, not changed, or is not enough information provided?
Explanation / Answer
Considering the given reaction and details. Kc decrease with the increase in temperature, which means reaction is exothermic.:
(1) The pressure of SiF4 is increased: Technically when pressure is increased, overall reaction pressure increases. Now according to Le- Chatelier's Principle,When pressure of reaction is increased, the reaction equilibrium shifts twards the reaction end with lower no of gaseous parts (considering all the other liquids and solids involved ar incompressible). Thus increase in pressure will result in shifting of equilibrium point backwards (towards reactants). The conc. of SiF4 and H2O increases whereas conc. of SiO2 and HF will decrease. Energy will be absorbed.
(2) If HF is added: Increase in concentration of HF will force the reaction backwards. Therefore The conc. of SiF4 and H2O increases whereas conc. of SiO2 and HF will decrease. Energy will be absorbed.
(3) If the amount of SiO2 is increased : Increase in concentration of SiO2 will force the reaction forward. The conc. of SiO2 and HF increases whereas conc. of SiF4 and H2O will decrease. Energy will be released.
(4) If the energy of the reaction is increased: Increase in energy of reaction will inhebit the forward reaction. The conc. of SiF4 and H2O increases whereas conc. of SiO2 and HF will decrease. Energy will be absorbed.
(5) If volume is doubled : According to Le- Chatelier's Principle, increase in volume will favour the reaction side with lower moles of gaseous particles (Reactants in this case). Therefore, the reaction will shift backwards. The conc. of SiF4 and H2O increases whereas conc. of SiO2 and HF will decrease.