Chapter 18 Reaction Rates
The numerical value of ∆G is ____ in spontaneous reactions because the system loses free energy; the numerical value of ∆G is ____ in non-spontaneous processes because the system requires that work be expended to make them go forward at the specified conditions.
negative, positive
In a first-order reaction, the reaction rate is directly proportional to the concentration of:
only one reactant
The ____ of a reaction is the power to which the concentration of a reactant must be raised to give the experimentally observed relationship between concentration and rate.
order
The law of disorder states that processes move in the direction of ____ disorder of randomness.
maximum
True or false: A process can be made 100% efficient.
False, seldom more than 70% efficient
True or false: The smaller the particle size, the larger the surface area of a given mass of particles.
True
What is entropy?
a measure of the disorder of a system
What is an intermediate?
a product of one step in a reaction mechanism and a reactant in the next step
The life time of an activated complex is
10⁻¹³s
what is a specific rate constant for a reaction?
A proportionality constant relating the concentrations of reactants to the rate of reaction.
Collision theory
Atoms, ions, and molecules can react to form products when they collide if the particles have enough kinetic energy.
How do you determine the reaction mechanism of a reaction?
By looking at the experiment
Le Châtelier's principle
If a stress is applied to a system in a dynamic equilibrium the system changes in a way that relieves the stress.
What happens when you put more reacting particles in a fixed volume?
Increases the concentration of reactants and the frequency of collision
How do you show catalysts in a chemical equation?
It is written above the yield arrow
Why is an activated complex sometimes called a transition state?
Its brief existence ends with the reformation of the reactants or with the formation of products
Why is an exothermic reaction accompanied by an increase in entropy considered a spontaneous reaction?
both factors are favorable
The minimum amount of energy that particles must have in order to react is called:
activation energy
How are rates of chemical change expressed?
amount of reactant changing per unit of time
A ____ is a substance that increases the rate of reaction without being used up itself during the reaction.
catalyst
Stresses that upset the equilibrium of a chemical system include changes in:
concentration, pressure, and temperature
The equilibrium position of a reaction is given by the relative ____ of the system's components at equilibrium.
concentrations
What does a catalyst do?
decreases the activation energy
What are some ways to increase the surface area of solid reactants?
dissolve them or grind into a fine powder
What are non-spontaneous reactions?
do not favor the formation of products at the stated conditions
An ____ reaction is one in which reactants are converted to products in a single step.
elementary
Some factor other than ____ change must help determine whether a physical or chemical process is spontaneous.
enthalpy
True or false: Chemical equilibrium is a state in which the forward and reverse reactions take place at different rates
false
Is the following sentence true or false: Entropy decreases when a substance is divided into parts?
false, entropy INCREASES
True or false: A rate law is an expression relating the rate of a reaction to the concentration of products
false; relates the rate to the concentration of reactants
How does increasing pressure affect a chemical system?
favors the production of a smaller number of molecules of gas
Four spontaneous reactions
ice melting, fireworks, sugar and oxygen produce CO₂ and H₂O, decomposition of carbonic acid in water
Does entropy tend to increase or decrease in chemical reactions in which the total number of product molecules is greater than the total number of reactant molecules?
increase
Entropy tends to ____ when temperature increases.
increase
The main effect of increasing the temperature of a chemical reaction is to ____ the number of particles that have enough kinetic energy to react when they collide.
increase
An ____ is a substance that interferes with the action of a catalyst.
inhibitor
An activated complex is the arrangement of atoms at the ____ of the activation-energy barrier.
peak
The equilibrium constant is the ratio of ____ concentrations to ____ concentration at equilibrium, with each concentration raised to a power equal to the number of ____ of that substance in the balanced chemical equation.
product, reactant, moles
Which arrangement of atoms contains the least amount of energy?
products
Spontaneous reactions are reactions that occur naturally and that favor the formation of ____ at the specified conditions.
products and release free energy
A value of keq greater than one means that ____ are favored over ____. A value of keq less than one means that ____ are favored over ____.
products, reactants; reactants, products
When you add a product to a reversible reaction, the reaction is always pushed in the direction of ____. When you remove a product, the reaction is pulled in the direction of ____.
reactants, products
In a typical reaction, as time passes the amount of _____ decreases and the amount of _____ increases.
reactants; products
What is a reaction progress curve?
shows an activation energy peak for each elementary reaction
Put the phases of matter in order of increasing entropy
solid, liquid, gas
The Gibbs free-energy change (∆G) is an indication as to whether a process is ____ at a given temperature.
spontaneous
Changes in rate depend on conditions such as
temperature, concentration, particle size, use of a catalyst
What are the exponents in the equilibrium-constant expression?
the coefficients in the balanced chemical equation
What do the square brackets indicate in the equilibrium constant expression?
the concentrations of substances in moles per liter
What is the difference between the reaction progress curve and the chemical equation for a reaction?
the graph contains the intermediates and activated complexes instead of just the reactants and products
What happens in a reversible reaction?
the reaction occurs in both directions at the same time so both reactants and products are produced
What determines whether a reaction is spontaneous?
the size and direction of enthalpy changes and entropy changes
What determines the rate of a multi-step reaction?
the slowest step will determine the rate of the overall reaction
True or false: A reaction mechanism includes all of the elementary reactions of a complex reaction
true
True or false: Increasing the temperature of a chemical reaction causes the equilibrium position of the reaction to shift in the direction that absorbs heat
true
True or false: Particles lacking the necessary kinetic energy to react bounce apart unchanged when they collide?
true
True or false: Some reactions that are non-spontaneous at one set of conditions may be spontaneous at other conditions
true
True or false: The value of keq for a reaction depends on the temperature
true
True or false: A non-spontaneous reaction, one in which the products are not favored, has heat changes, entropy changes, or both working against it.
true, randomness is not favored
Free energy is energy that is available to do:
work
What is the symbol for a change in entropy?
∆S
