chemistry unit 13

nature of reactants

The stability of reactants, types of bonds involved, and states of matter all affect reaction rates.

as reaction progress...

[reactants] decreases; [products] increases

inhibitors

are catalysts that slow the rate of reaction. For example, food preservatives slow the rate of decay reactions.

enzymes

biological catalyst are large macromolecules - usually proteins - that catalyze metabolic reactions in living organisms

reaction rate is usually measure by

change in concentration (M or mol/L) of products (or reactants) per unit time in seconds. Therefore, the unit for reaction rate is mol/Ls.

for gases only

decreasing the volume (L) occupied increases the concentration of the reactants and leads to an increase in reaction rate. Changing the pressure on gases also changes the concentration of gaseous reactants.

ineffective Collisions

do not allow reaction to occur because there is insufficient energy to form the activated complex; in these instances, the atoms rebound (bounce off each other) and reform the reacting substances.

reactant particles must be

effective, meaning they meet two requirements: Reacting particles must collide with the proper orientation. must collide with sufficient energy

heterogeneous catalyst

exists in a different phase than the reacting particles. For example, solid metals are used in catalytic converters in cars to convert toxic gaseous emissions to non-toxic gases.

homogenous catalyst

exists in the same phase as the reacting particles. For example, gaseous chloride ions from CFCs catalyze the destruction of ozone gas in the atmosphere.

reaction non spontaneous

in the opposite direction (for example, the reverse or backward reaction).

decreasing particle size

increases the surface area of the reactant particles available for collision. As a result, more collisions will occur, and as collision frequency increases, the reaction rate increases.

catalyst

is a substance that changes the rate of reaction without being consumed by the reaction.

energy in the activation complex is

is higher than that of the reactants or products and is often referred to as a high energy state

Activation energy

is the minimum amount of energy that must be added to the reactants in order for the activated complex to form.

collision frequency

is the total number of collisions, both effective and ineffective, that occur per second.

the energy comes from

kinetic energy of the reactant particles, causing the bonds in the reactants to break and allowing the atoms to rearrange.

low activation energy

means most of the reacting particles have sufficient kinetic energy to react, and the reaction will occur rapidly (slow reaction rate

high activation energy

means most of the reacting particles will not have enough energy to react, and the reaction will most likely occur very slowly (fast reaction rate).

reaction rate

measures how quickly or how slowly reaction occurs; it indicates the rate at which products are formed in a specific time interval or the rate at which reactants are consumed over a time interval.

spontaneous

process is a physical or chemical change that occurs under a specific set of conditions without continuous external support. Once sufficient activation energy is provided, spontaneous reactions tend to proceed to completion

effective collisions

result in the formation of products as the atoms move from the activated complex to form new bonds. Potential energy is released and becomes heat that is absorbed by the surroundings.

second law of thermodynamics

states that every spontaneous change in the universe increases the entropy of the universe

additional energy can be added by different sources like

such as flame, spark, heat, or radiation.

entropy

symbolized by S, is a measure of the possible ways that the energy of a system can be distributed. It is also referred to as a measure of the disorder or randomness of a system. increases as the number of possible arrangements of particles increase

substances with strong bonds

tend to have high Ea and react more slowly than substances with weaker bonds.

chemical reactions requires

that the bonds in the reactant substances be broken, the atoms be moved into new arrangements, and new bonds be formed in the products

when a reactant are in liquid and gas and are mixed thoroughly

the particles collide more frequently than if one or both reactants are solids.

most reactions take place in solution

the type of solvent and its viscosity can affect the reaction rate.

alternate pathway

to form products from reacting substances. requires less energetic collisions, and more reacting particles are able to achieve effective collisions and form products. In other words, the reaction pathway for the catalyzed reaction has lower activation energy

equilibrium state

when a reaction's forward progress (reactants forming products) is perfectly balanced with the reverse process (products changing back into the reactants)

surface area exposed

As the number of reactant particles available for collision changes, the reaction rate changes

temperature

Changing the kinetic energy of particles affects rate. Increased temperature increases the collision frequency. More importantly, the number of particles having kinetic activity ≥ Ea increases; therefore, the number of effective collisions increases.

concentration

Changing the number of reactant particles usually has the greatest effect on reaction rate. As explained by collision theory, having more particles present increases the number of collisions per unit time; therefore, the collision frequency increases, the number of effective collisions increases, and the reaction rate increases.

collision theory

Collision theory explains why reaction occurs between atoms, ions, and/or molecules at the particle level. Collision theory then allows the prediction of conditions necessary for successful reaction. Unit

spontaneous does not include

Energy transfer (if reaction releases or absorbs energy), or Reaction rate (how quickly or slowly reaction occurs)

entropy

S): reactions tend to be spontaneous if disorder increases (+ΔS)

activated complex

(AKA transition state) is a temporary and unstable jumble of particles from all the reactant molecules.

gibbs free energy

(G), measured as ΔG, is the amount of energy available for work, which refers to a transfer of energy to or from a system by any means other than heat. The more negative the value ΔG, the more spontaneous the reaction.

enthalpy

(H): a decrease in energy (-ΔH) is thermodynamically favorable