The reaction Si(s) + 4 HCl(g) SiCl_4 (g) + 2 H_2 (g) is an exothermic reaction w

Question

The reaction Si(s) + 4 HCl(g) SiCl_4 (g) + 2 H_2 (g) is an exothermic reaction with Delta H degree = -288 kJ. A mixture of the two reactants and the two products in a cylinder equipped with a piston is allowed to stand until equilibrium is reached. Predict the effects of the following actions on the position of the equilibrium. The effect of each of the following actions on the reaction mixture, which may be a shift to the left, a shift to the right, or no shift, should be entered in the right-hand column.

Explanation / Answer

Apply Le-chatelier Concepts of equilibrium

- it states that equilibrium will be shifted toward cunter-balancing the effect

so

a)

removal of H2, a products, will make the reaction to produce even more SiCl4+ H2, from reactants to counterbalance the shift

b)

addition of Si(s) will not likely affect, since it is a solid

K = [SiC4][H2]^2 /[HCl]^4

Clearly, the silicon is not included in the equilbrium

there is no shift

c)

If we reduce Volume, we increase Pressure

Increase in pressure will favour the LEAST moles of gases

this is for products, 1+2 = 3 moles, vs 4 moles in reactants

so more poducts will be produced, shift goes to right

d)

Addition of Argon gas, will incrase the pressure of the system

Increase in pressure will favour the LEAST moles of gases

this is for products, 1+2 = 3 moles, vs 4 moles in reactants

so more poducts will be produced, shift goes to right

e)

lowering T will help this reactions

since this is exothermic ( from - HRxn value) the equilibrium will shift towad right

f)

addition of a catalyst will NOT affect equilibrium, only affects the rate at which it is obtained

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