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H 2 O + CO H 2 + CO 2 As a reaction proceeds, the concentration of reactants declines, and the concentration of products increases.

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Presentation on theme: "H 2 O + CO H 2 + CO 2 As a reaction proceeds, the concentration of reactants declines, and the concentration of products increases."— Presentation transcript:

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2 H 2 O + CO H 2 + CO 2 As a reaction proceeds, the concentration of reactants declines, and the concentration of products increases

3 H 2 O + CO H 2 + CO 2 For reactions with a significant reverse reaction, the decrease in reactant concentration causes a decrease in the rate of the forward reaction. Also, the increase in product concentration causes a decrease in the rate of the forward reaction.

4 H 2 O + CO H 2 + CO 2 At some point, the rates of the forward and reverse reactions become equal and constant. This is called the equilibrium state because the changes in concentration and rate reach a constant, steady state.

5 In the equilibrium state, the concentration of all reactants and products also remains constant. The concentrations are constant but this does not mean the concentrations are equal.

6 The state of equilibrium is a a steady-state system It remains constant unless acted upon by the surroundings.

7 Equilibrium The state of a reaction where the concentrations of all reactants and products remain constant over time The state of a reaction where the forward and rate of the reaction are equal

8 Equilibrium Expression Since the concentration of all reactants and products remains unchanged during equilibrium, the ratio of the product concentrations to the reactants concentrations is a constant. This ratio is used to describe the equilibrium state for a particular reaction at a specified temperature. The ratio is called the equilibrium constant ( K) K c if concentrations are measured in molarity K p if concentrations are measured in pressure

9 Equilibrium constant = K = [ C ] 3 [ D ] [ A ] 2 [ B ] The coefficients of the balance equation are automatically included in the equilibrium expression Equilibrium Expression For the reaction: 2 A + B 3 C + D

10 1. Pure Solids Since concentration is constant for a solid, a solid reactant or product is left out of the equilibrium equation 2. Pure liquids and Solvents Since the concentration of a pure liquid or solvent is relatively constant, a pure liquid or solvent (reactant or product) is left out of the equilibrium equation

11 CaCO 3 (s) CaO (s) + CO 2 (g) H 2 CO 3 (aq) + H 2 O (l) HCO 3 - (aq) + H + (aq) K = [CO 2 ] K= [HCO 3 - ] [H + ] [H 2 CO 3 ]

12 Dinitrogen tetroxide decomposes on heating to nitrogen dioxide in a reversible reaction. At equilibrium, a two liter flask at 100 ° C contains mol dinitrogen tetroxide and mol of nitrogen dioxide. Determine the equilibrium constant for the reaction at 100° C. N 2 O 4 2 NO 2 [N 2 O 4 ] = M [NO 2 ] = M note the absence of units for K K = [NO 2 ] 2 = [0.030] 2 = 0.20 [N 2 O 4 ] [0.0045]

13 Tin II oxide reacts with carbon monoxide by the following reaction: SnO 2 (s) + 2 CO (g) Sn (s) + 2 CO 2 (g) Measurements indicate that 10 grams of SnO 2 placed in a chamber filled with CO gas results in a partial pressure of 2.50 atm for carbon monoxide and a partial pressure of 3.12 atm for carbon dioxide at equilibrium. Write the equilibrium expression for the reaction. K p = (P CO2 ) 2 (note that the equilibrium constant is K p (P CO ) 2 since the concentration is in pressure. What is the value of the equilibrium constant K p K p = (P CO2 ) 2 = ( 3.12) 2 = 1.56 (P CO ) 2 (2.50) 2 How would the equilibrium concentrations of CO and CO 2 change if the amount of SnO 2 is increased to 20 g? No change


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