ICE table. How does one know if the x is positive or negative for the products and reactants? this question is contradicting what i thought because the x is negative in the reactants yet one reactant starts with zero concentration.

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    See explanation.
    I am not sure why the answer is missing a very essential point which is teaching the student Le Chtelier’s principle . Maybe this is not a grade 12 question!!!!
    The student could easily deduce that since the ##[I_2]=0M## the equilibrium will shift toward the direction of making ##I_2## and therefore to the left and in this case the ICE table is written as follows:
    ## H_2(g)+I_2(g)rightleftharpoons 2HI(g)##
    ##Initial 8M 0M 2.4M##
    ##Change +x +x -2x##
    ##Equilibrium 8+x x 2.4-2x ##
    In this case ONLY ##color(green)(positive)## values of ##x## will be accepted.
    However the way the answer is written is that he will assume that the equilibrium is shifting to the right and in this case ##x## will be ##color(green)(positive)## however if his assumption is wrong ##x## will be ##color(red)(negative)## and this is the case that is why the ##[HI]## dropped from ##2.4M## to ##2.2M##.

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