When doing an ICE Chart in Chemistry, when do you know whether the C is a negative or positive?
I was told if the problem gives us reactant concentrations and no product concentration then the reaction goes forward and make the reactant lose and the product gain for example I2 (g) + H2 (g) ----> 2HI
However, what if it's 2BrCl -----> Br2 + Cl2 , would it still apply?
Yes, in that case it still applies. If reactants ar given and zero produccts are given common sense tells you that it MUST go the right and the reactant(s) lose and the product(s) gain.
The second possibility is that you have zero reactants but you start with the product. In that case common sense tells you it MUST go to the left and form reactants at the expense of the product(s).
The third case involves say you have a reaction like
2A + B ==> C and values are given for A and C or even A, B and C. Then common sense doesn't help much. What you do in that case is set up Qc, plug in the numbers and see if Qc is <, =, or > Kc.
If Qc<Kc the equilibrium point is to the right(more products and fewer reactants). If Qc > Kc, the reverse. If Qc = Kc the reaction is at equilibrium.
In an ICE (Initial-Change-Equilibrium) chart, the "C" stands for the change in concentration of the species involved in a chemical reaction. Whether the change in concentration is positive or negative depends on the stoichiometry of the reaction.
If you have a reaction like I2 (g) + H2 (g) ----> 2HI, and you are given the initial concentrations of I2 and H2 but not the concentration of HI, you can deduce that this is a forward reaction. In a forward reaction, reactants are consumed, leading to a decrease in their concentrations, while products are formed, leading to an increase in their concentrations. Therefore, the change in concentration for I2 and H2 would be negative (-), indicating a decrease in their concentrations, while the change in concentration for HI would be positive (+), indicating an increase in its concentration.
Now, let's consider the reaction 2BrCl -----> Br2 + Cl2. In this case, you are not given any initial concentrations or the concentration of any products. However, based on the stoichiometry of the reaction, you can still determine the sign of the change in concentration.
Since the reaction only has one reactant and two products, it suggests that the reaction is going in the reverse direction (reactants are being formed, products are being consumed). Therefore, the change in concentration for Br2 and Cl2 would be negative (-), indicating a decrease in their concentrations, while the change in concentration for BrCl would be positive (+), indicating an increase in its concentration.
In summary, the sign of the change in concentration (C) depends on whether the reaction is going in the forward or reverse direction, as determined by the stoichiometry of the reaction.