ICE table
An ICE table tracks Initial, Change and Equilibrium amounts to find an unknown equilibrium concentration. Let x be the change, use the coefficients for each species, then plug the equilibrium row into the K expression and solve for x.
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Analogy
Like a ledger: start balance, transactions, final balance.
Example
Start: [H₂] = [I₂] = 1.0, [HI] = 0Change: −x, −x, +2x(2x)² / (1.0 − x)² = 64x = 0.80, [HI] = 1.6 M
In practice
Chemists use ICE tables to find how much of a weak acid or a gas mixture ends up as products.
Practice
Flashcards
- What does ICE stand for?Initial, Change, Equilibrium.
Interview questions
- For H₂ + I₂ ⇌ 2HI with K = 64, find equilibrium concentrations starting from 1.0 M H₂ and 1.0 M I₂.
- Set up an ICE table
- (2x)²/(1−x)² = 64
- Take square root: 2x/(1−x) = 8
- x = 0.80, so [HI] = 1.6 M and [H₂] = 0.20 M
Questions people ask
When can I ignore x in an ICE table?
If K is very small (below about 10⁻³) compared with the starting concentration, then x is tiny and 1.0 − x is almost 1.0. You can drop x from the subtraction. Check the answer: if x is under 5 percent of the starting amount, the shortcut is valid.
What if the ICE equation needs a quadratic?
If the shortcut isn't allowed, expand the equation into ax² + bx + c = 0 and solve with the quadratic formula. Choose the root that gives non-negative concentrations for every species. The other root is not chemically possible and should be discarded.