A reaction that can run toward products and also back toward reactants is described as reversible.
Missing Word
reversible
A reversible reaction can proceed in both directions. Only reversible reactions can reach a chemical equilibrium, where the two directions occur at equal rates.
Category: Dynamic Equilibrium
Question 2
Because molecules keep reacting in both directions at equal rates, chemical equilibrium is described as dynamic rather than static.
Missing Word
dynamic
Dynamic means ongoing activity. At equilibrium the concentrations hold steady, yet reactant and product molecules continue to interconvert.
Category: Dynamic Equilibrium
Question 3
An equilibrium in which every reactant and product is a gas, or every one is dissolved in the same solution, is called homogeneous.
Missing Word
homogeneous
A homogeneous equilibrium has all of its species in a single phase, such as an all-gas reaction or a reaction entirely in aqueous solution.
Category: Equilibrium Expressions
Question 4
The decomposition of solid calcium carbonate into solid calcium oxide and carbon dioxide gas is an example of a heterogeneous equilibrium.
Missing Word
heterogeneous
A heterogeneous equilibrium involves species in more than one phase, here two solids and a gas. Only the gas appears in its equilibrium expression.
Category: Equilibrium Expressions
Question 5
A reaction that releases heat to its surroundings, so that heat can be treated as a product, is classified as exothermic.
Missing Word
exothermic
An exothermic reaction has a negative enthalpy change. Treating heat as a product predicts that heating shifts it toward reactants and cooling shifts it toward products.
Category: Le Chatelier's Principle
Question 6
Heating shifts the equilibrium of a heat-absorbing reaction toward its products, because heat acts as a reactant in an endothermic process.
Missing Word
endothermic
An endothermic reaction has a positive enthalpy change. Treating heat as a reactant predicts that heating shifts it toward products and raises K.
Category: Le Chatelier's Principle
Question 7
In the Haber process, nitrogen gas and hydrogen gas react at high pressure, with the product continually removed, to produce ammonia.
Missing Word
ammonia
Ammonia, NH3, forms from N2 and H2 in an exothermic reaction that has fewer moles of gas on the product side, so high pressure and removal of product increase the yield.
Category: Le Chatelier's Principle
Question 8
In an equilibrium constant expression, each concentration is raised to a power equal to its coefficient in the balanced chemical equation.
Missing Word
coefficient
The coefficient is the number placed in front of a formula in a balanced equation. It becomes the exponent on that species' concentration or partial pressure in Q and K.
Category: Equilibrium Expressions
Question 9
The only change in conditions that alters the numerical value of an equilibrium constant is a change in temperature.
Missing Word
temperature
Changing concentrations, pressure or volume, or adding a catalyst, can change the composition of the mixture but not K. Temperature changes K because it changes the forward and reverse rate constants by different amounts.
Category: Manipulating K
Question 10
A substance that lowers the activation energy of the forward and reverse reactions equally, so that equilibrium is reached sooner with no change in K, is a catalyst.
Missing Word
catalyst
A catalyst speeds both directions of a reversible reaction by the same factor. It shortens the time needed to reach equilibrium but leaves the equilibrium composition and the value of K unchanged.
Category: Le Chatelier's Principle
Question 11
In an equilibrium constant expression, the concentrations of the products appear in the numerator.
Missing Word
numerator
The numerator is the top of a fraction. K and Q both place product terms on top and reactant terms on the bottom, each raised to its coefficient.
Category: Equilibrium Expressions
Question 12
The equilibrium constant written in terms of the partial pressures of gases is symbolized Kp.
Missing Word
Kp
Kp uses partial pressures of gaseous species, while Kc uses molar concentrations. For gas-phase reactions the two are related through RT and the change in moles of gas.
Category: Equilibrium Expressions
Question 13
A table with rows for Initial concentrations, the Change in each concentration and the Equilibrium concentrations is called an ICE table.
Missing Word
ICE
ICE stands for Initial, Change, Equilibrium. The Change row follows the mole ratios of the balanced equation, and the Equilibrium row is substituted into the K expression.
Category: Equilibrium Calculations
Question 14
When the change x is too large to ignore, the equilibrium expression is often rearranged and solved with the quadratic formula.
Missing Word
quadratic
Many equilibrium expressions become a second-degree equation in x. If x is not small next to the starting amount, the quadratic formula gives two roots, and the one that leaves every equilibrium concentration positive is the answer.
Category: Equilibrium Calculations
Question 15
A reaction with a very small equilibrium constant has reactant terms in the denominator that are much larger than the product terms on top.
Missing Word
denominator
The denominator is the bottom of a fraction, where K places the reactant concentrations. When those terms greatly outweigh the product terms, K is much less than 1 and reactants are favored.
Category: Equilibrium Expressions