Multiple Choice
Which of the following is the correct equilibrium constant expression for the reaction: 3H+(aq) + PO4^3-(aq) ⇌ H3PO4(aq)?
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16. Chemical Equilibrium
Equilibrium Constant K
Multiple Choice
What is the value of the equilibrium constant (K_w) for the autoionization of pure water at 25°C?
A
1.0 × 10^{-10}
B
1.0 × 10^{-7}
C
1.0 × 10^{-14}
D
1.0 × 10^{-4}
Verified step by step guidance1
Understand that the equilibrium constant for the autoionization of water, denoted as \(K_w\), is defined by the reaction: \(\mathrm{H_2O (l) \rightleftharpoons H^+ (aq) + OH^- (aq)}\).
Write the expression for the equilibrium constant \(K_w\) as the product of the molar concentrations of the hydrogen ions and hydroxide ions: \(K_w = [H^+][OH^-]\).
Recall that at 25°C, pure water is neutral, meaning the concentration of hydrogen ions \([H^+]\) equals the concentration of hydroxide ions \([OH^-]\).
Use the known concentration of hydrogen ions in pure water at 25°C, which is \(1.0 \times 10^{-7}\) M, and substitute into the expression: \(K_w = (1.0 \times 10^{-7})(1.0 \times 10^{-7})\).
Multiply the concentrations to find \(K_w = 1.0 \times 10^{-14}\), which is the equilibrium constant for the autoionization of water at 25°C.
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