Ch. 5: Alkenes, Thermodynamics, and Kinetics Flashcards

Question

What is entropy?

Answer 1

A measure of the freedom of motion in a system. Restricting the freedom of motion of a molecule decreases its entropy. Por ejemplo, in a reaction in which two molecules come together to form a single molecule, the entropy of the product will be less than the entropy of the reactants because two separate molecules can move in ways that are not possible when they are bound together in a single molecule. In such a reaction, delta S will be negative. In a reaction in which a single molecule is cleaved into two separate molecules, the products will have greater freedom of motion than the reactant and delta S will be positive.

Answer 2

if an equilibrium is disturbed, then the system will adjust to offset the disturbance. A way to ensure the value of the equilibrium constant remains constant.

Answer 3

A reaction is exergonic when it releases energy to the environment. The reactants have more free energy (delta G) than the products, so energy is released as the reaction proceeds.

Answer 4

Energy is stored in the products of a reaction. The reactants have less energy than the products, so energy must be added to make the reaction happen.

Answer 5

Endergonic and exergonic refer to free energy changes (delta G). Endothermic and exothermic refer to the changes in internal energy of molecules, measured as heat given off or taken up, delta H.

Answer 6

The addition of hydrogen to a compound is a reduction reaction. This type of reaction increases the number of C--H bonds and/or decreases the number oof C--O, C--N, or C--X bonds (X=halogen)

Answer 7

The addition of a hydrogen is called hydrogenation. Because hydrogenation reactions require a catalyst, they are called catalytic hydrogenation.

Answer 8

Hydrogen is absorbed on the surface of the metal and that the alkene interacts with the metal by overlapping its p orbitals with the vacant orbitals of the metal. All the bond-breaking and bond-forming events occur on the surface of the metal. As the alkane product forms, it diffuses away from the metal surface.

Answer 9

The heat released in a hydrogenation reaction. it is customary to give it a positive value even though hydrogenation reactions are exothermic. The heat of hydrogenation is the value of delta H without the negative sign.

Answer 10

As the number of alkyl substituent groups attached to the sp2 carbons increases, the stability of the molecule increases. ( can also say that the stability of an alkene increases as the number of hydrogens bonded to its sp2 carbons decreases)

Answer 11

When large groups are on the same side of the double bond, as in a cis isomer, their electron clouds can interfere with each other, causing steric strain in the molecule. Steric strain makes a compound less stable. When large groups are on opposite sides of the double bond, as in a trans isomer, their electron clouds cannot interact, so there is no destabilizing steric strain.

Answer 12

The energy barrier of a reaction. It is the difference between the free energy of the transition state and the free energy of the reactants. As this value decreases, the rate of reaction increases. Thus, anything that makes the reactants less stable or makes the transition state more stable will make the reaction go faster. delta G dd = (free energy of the transition state) - (free energy of the reactants)

Answer 13

1) The number of collisions that take place between the reaction molecules in a given period of time. The rate of the reaction increases as the number of collisions increases. 2) The fraction of collisions that occur with sufficient energy to get the reacting molecules over the energy barrier. If the free energy of activation is small, then more collisions will lead to reaction than if the free energy of activation is large. 3) The fraction of collisions that occur with the proper orientation. 2-Butene and HBr will react only if the molecules collide with the hydrogen of HBr approaching the pi bond of 2 butene. If a collision occurs with the hydrogen approaching a methyl group of 2-butene, no reaction will take place, regardless of the energy of collision.

Answer 14

When you know the relationship between the rate of a reaction and the concentration of the reaction, you can write the rate law for the reaction. The rate is proportional to the concentration of the reactants.

Answer 15

This equation relates the rate constant of a reaction to the experimental energy of activation and to the temperature at which the reaction is carried out.

Answer 16

The rate constant tells us how easy it is to reach the transition state (how easy it is to get over the energy barrier). Low energy barriers are associated with large rate constants. High energy barriers are associated with small rate constants. The rate of a reaction is a measure of the amount of product that is formed per unit of time. The rate of reaction depends on concentration, whereas the rate constant is independent of concentration.

Answer 17

A chemical species that is a product of one step of a reaction and a reactant for the next step. Intermediates have fully formed bonds.

Answer 18

represent the highest-energy structures that are involved in the reaction. They exist only fleetingly, and they can never be isolated.

Answer 19

If a reaction has two or more steps, the step that has its transition state at the highest point on the reaction coordinate is the rate-determining step. The rate-determining step controls the overall rate of reaction, because the overall rate cannot exceed the rate of the rate-determining step.

Answer 20

A catalyst increases the rate of reaction by giving the reactants a new pathway to follow-- one with a smaller delta G dd. In other words, a catalyst decreases the energy barrier that must be overcome in the process of converting the reactants to products. A catalyst does not change the relative concentrations of products and reactants when the system changes equilibrium. Therefore, it does not change the amount of product formed; it changes only the rate at which it is formed.

Answer 21

Most biological catalysts are proteins called enzymes. Enzymes are chains of amino acids linked together by covalent bonds. Each biological reaction is catalyzed by a different enzyme.

Answer 22

the reactant of an enzyme-catalyzed reaction

Answer 23

The enzyme binds to the substrate in a pocket of the enzyme called the active site. All bond-making and bond-breaking steps of the reaction occur while the substrate is bound to the active site.