Introduction to General Chemistry III

All of the chemical reactions described in this lecture can be characterized by kinetics (define). Kinetics is a complicated field with many opposing theories as to how reactions proceed, but the MCAT® will only test kinetics as it relates to _____ _____

Kinetics deals with the rate of a reaction as it moves toward ______, while thermodynamics deals with the balance of ______ and ______ after they have achieved equilibrium.

The differences between kinetic and thermodynamic properties of a reaction can be exploited to favor certain products of a reaction in a process called _____ versus ______ control of a reaction. Many reactions have several possible products, each favored by different reaction conditions.

The thermodynamic product is more ____, but it requires a higher _____ _____ and is produced more _____. The kinetic product is less _____ but can be formed more _____ because the required energy input is _____. _____ temperatures drive the reaction towards the thermodynamic product; _____ temperatures favor the kinetic product.

The reacting molecules must _____ for a chemical reaction to occur. However, the rate of a given reaction is usually much _____ than the frequency of ______. This indicates that most ______ do not result in a reaction. Only ______ that meet certain criteria will facilitate a reaction.

Remember that kinetic energy is energy of _____. In a given sample of a compound, each particle is moving at a different _____. Only particles with sufficient _____ will have the kinetic energy needed to overcome the _____ _____.

Explain the two requirements for a given collision to initiate a reaction

The product of the collision frequency z, the fraction of collisions having the effective spatial orientation p (called the _____ _____), and the fraction of collisions having sufficient relative energy e^-E_a/^RT (where E. is the _____ _____ and R is the ____ ______ 8.314 J K^-1mol^-1) gives the rate constant k of a reaction. This relationship is called the Arrhenius equation: k = zpe^-E_a/RT (This is often written as k = Ae^-E_a/RT , where A replaces the product zp.)

The term e-^E_a/RT can be rewritten as 1/e^E_a/RT. An increase in E, will therefore _____ the denominator and reduce the value of k.

The value of the rate constant is affected by _____, ______ and ______. Pressure dependence is typically relevant only for _____, for which higher pressure _____ the rate constant. Catalysts _____ the activation energy, and therefore ______ the rate constant.

Temperature dependence is demonstrated by the Arrhenius equation. Because temperature is a proxy for _____ ____, the number of collisions that can overcome the activation energy _____ with temperature. This means that the rate constant k _____ with increasing temperature. As demonstrated by the rate law, discussed later in this lecture, the rate constant is _____ _____ to the rate of a reaction. Therefore, the rate of a reaction _____ with temperature mainly because higher temperatures allow for more _____ with sufficient relative kinetic energy in a given amount of time. Higher temperatures increase the rate of both the _____ and _____ reactions.

The temperature dependence of rate is demonstrated in Figure 1.23, which compares two samples of identical mixtures reacting at different temperatures. The area under any section of the curve represents the relative number of _____ in that kinetic energy range. The energy range of interest is above the _____ ______ _____, or to the _____ of the red line labeled Ea.

The area to the right of this line is _____ for the reaction at the higher temperature (i.e. the blue area under the higher temperature curve is much _____ than the striped area under the lower temperature curve). In reality, the activation energy itself changes slightly depending on ______. However, these changes are _______ and can be ignored on the MCAT®.

Define reaction rate

The MCAT®will only test the kinetics of reactions occurring in _____ or in ideally _____ _____ at constant temperature. Rates are most often represented in units of ______ per second (M s-1 or mol L - I s- 1) because they represent the change in _______ of the reactants and the products over time.

The _____, ______ and ______ of substances in the reaction system can affect the rate of a reaction. Recall that the rate of reactions increases as temperature ______. The effects of pressure on reaction rates are usually _____ enough to be ignored.

The rate of a reaction can be viewed in terms of the change in concentration of any one of the substances involved in the reaction (the disappearance of reactants or the appearance of products). Consider the following elementary reaction, where the lower case letters are the _____ _____ of the balanced equation:
aA + bB → cC + dD

An ______ reaction is a reaction that occurs in a single step. The stoichiometric coefficients of an elementary equation give the ______ (define) of the reaction

The three most common molecularities are ______, ______ and ______. The molecularity of the elementary reaction above is given by a+ b. If both a and b were equal to one, the reaction would be ______. Most reactions are not elementary reactions, what are they instead?

The idea that rate can be expressed as the disappearance of reactants or the appearance of products is summarized in a formula. For the above reaction, the average reaction rate over the time interval t is written as:

The negative signs indicate that the concentration of reactants is _____ as the reaction moves ______. The lower case letters in the denominator represent the ______ ______ and are used to compare the rate of ______ use and ______ formation as the reaction moves ______.

The coefficients must be accounted for in this method of describing the reaction rate because they establish the _____ relationship between ______ and ______. In the sandwich example, the coefficients show that the rate at which bread slices are used up is only ____ of the rate at which sandwiches are produced; ____ slices of bread are required for one sandwich. The rate at which cheese slices are used up is the same as the rate at which ______ are produced: for every slice of cheese, one sandwich is produced. Sandwiches and cheese slices have the same ______.

The same ideas apply to this chemical reaction:
N₂O₅(g) → 4NO₂(g) + O₂(g)

Only one unit of O2 is produced for every ____ units of N2O5 that are used up. The rate expression shows that N2O5 disappears at ____ the rate that O2 appears. The rate equation given above is strictly correct only for an ______ reaction, but it is a good approximation for a multistep reaction if the concentrations of any intermediates are ____.

Intermediates are species that are _____ of one step and _____ of a later step in a multistep reaction. Because they get used up before the end of the reaction, they are not shown in the overall _____ _____. Intermediates are often present only in ____ concentrations.

Notice that the rate equation above gives only the _____ _____ _____ for a time interval t during the reaction. It does not account for changes in the reaction rate at any ______ during that time interval.

In the initial moments of a reaction, the concentration of reactants is very _____ relative to the concentration of products, and the rate of the reverse reaction is _____. Most chemical reactions are reversible: as the ______ are formed, they begin to react to re-form the ______. This complicates the calculation of reaction rates, since rates rely on the ______ of reactants. Therefore reaction rates are usually determined using only the ______ observed by experimenter in the initial moments of the reaction.

These initial reaction rates are used to derive an expression for reaction rate known as the rate law, which incorporates only the concentrations of ______:
rate forward = k_f [A]^a[B]^β 
where k_f is the rate constant for the _____ reaction, a and β are the _____ _____ of each reactant, and the sum a + β is the _____ ____ of the reaction.

rate forward = kf [A]^α[B]^β 

α and β are related to the number of molecules that must _____ for a particular elementary reaction. If the reaction is elementary, α = a and β = b (i.e., the reaction order for each reactant is equal to the _____ _____). If the reaction is not elementary, the exponents of the rate law must be determined ______. Such experimental results would be given by the MCAT®. The rate law can be used to determine how changes in _____ ______ affect the reaction rate.

How to find the order each reactant 

Adding the exponents shows that the reaction is ____ order overall (1 + 2 + 0 = 3). Notice that the coefficients in the balanced chemical equation do not correspond to with the _____ of each reactant. Once the rate law has been derived from the experimental data, the rate and concentrations from any of the experiments can be plugged into the rate law to solve for the ____ ____ ___.

The rate law equation shows that the rate can be _____ by increasing the concentration of the reactants. T his makes sense in the context of the ______ model. The greater the concentration of a species, the _____ likely it will collide with the other reactants.

Reaction orders indicate how changes in the ______ ______ influence the reaction rate. The order of each ______ indicates the particular influence of that reactant, while the order of the ______ _____ provides more general information about the relationship between ______ ______ and ______ _____.

The order with respect to any reactant is that reactant's ______ in the rate law. The order of the overall reaction is the _____ of the exponents in the rate law.

A _____ order reaction has only one reactant raised to the power of 1 in the rate law. Sometimes a concentration will be written without an exponent and a _____ is inferred.

If a reactant does not appear in the rate law, the exponent is ____, and the reaction rate ______ depend on that reactant. In an overall zero-order reaction, the reaction rate is ______ of the concentration of any ______. This occurs in ______-______ reactions when the concentration of the substrate far outweighs the concentration of the enzyme. All of the enzyme catalytic sites get saturated with ______ and the addition of more substrate has no effect on ______ _____.

For a multistep reaction, the overall reaction can be broken down into two or more _______ reactions. The ______ of these elementary reactions determines the rate equation. In the rate law example from the previous few pages, it is possible that the reaction was a multistep reaction with a ____ step involving only A and B and a ____ step involving C. The slow step determines the _____ _____, which could explain why the concentration of ___ does not affect the rate of the reaction.

In a first-order reaction, the reaction rate is _____ _____ to the concentration of a single reactant. An example of a first-order reaction is ______ ______, described later in this lecture.
A → products rate= k_f[A]

Second- and third-order reactions come in ____ types. In one type, the reaction rate is proportional to a _____ ______ concentration raised to the _____ or _____ power:
2A →products  rate= k_f[A]² (second order)
3A →products  rate= k_f[A]³ (third-order)

In the second variety, the reaction rate is proportional to the product of the concentrations of ______ ______:
A+ B →products rate= k_f[A][B] (second-order)
A+ B → products rate= k_f[A][B]² (third-order)
A+ B + C → products rate= k_f[A][B][C] (third-order)

Many complex reactions can be broken down into elementary steps. Since the rate of the slowest elementary step determines the rate of the overall reaction, this step is called the ____-______ step. If the first step is the ____ step, the rate law is derived from this step. If another step is the ____ step, it is still the rate-determining step, but the steps prior to this rate determining step will, also _____ to the rate law. Steps after the slow step _____ contribute to the rate law.

 
_____ these two equations together gives the original equation. Elementary steps must ____ to give the complex overall reaction. Since the first step is the ____ step, the rate law for the overall reaction is given by this step and is:
rate = k₁[NO₂]²

Remember, using coefficients from a balanced equation for the exponent in the rate law only works if the equation is ______. The exponent for [NO₂] is 2 because the rate-determining step is an ______ equation. In that elementary equation, two NO₂ molecules collide to create a reaction. The rate law above assumes that there is _____ contribution from the reverse reaction and that the concentration of CO is sufficient for the ____ step to occur.

Catalysts (define) increase the rate of both the _____ and the ______ reactions. 1)They can _____ product selectivity and 2)_____ energy consumption. 3)A catalyst may _____ the activation energy, E., 4)_____ the steric factor (p from the Arrhenius equation), or 5)both. Increasing the steric factor ______ the number of favorable collisions.

Most catalysts work by lowering the ______ ______. The reaction rate depends exponentially on the _____ _____. When the activation energy is lowered, more collisions have sufficient _____ _____ to result in a reaction. This leads to more reactions and a(n) ______ in the overall reaction rate. This effect is shown in the energy vs. reaction coordinate diagram in Figure 1.25.

A catalyst provides an alternative reaction mechanism that competes with the ______ mechanism. Because a catalyst lowers the activation energy, it creates a different _____ _____, which increases the rate of both the ______ and the ______ reactions. A catalyst cannot alter the _______ or the _____ _____ of a reaction.

A catalyst can be either ______ or ______. A heterogeneous catalyst is in a different _____ than the reactants and products, such as when gas or aqueous particles react on a _____. In this case, the particles adsorb (stick to) to the surface of the solid due to _______ ______.

The rate of catalysis depends on the strength of attraction between the ______ and the _____. When it is too weak, there is not enough ______, and the catalyst has little effect on the reaction rate. When it is too strong, too much _____ is required to remove the reactant, and therefore the catalyst _____ facilitate the reaction. The more adsorption that occurs, the ______ the reaction rate. Thus, reaction rates can be enhanced by increasing the surface area of a catalyst. Often this is done by grinding a solid into a ______.

A homogeneous catalyst is in the same _____ as the reactants and products, usually as a gas or liquid. _____ ____ or _____ _____ often act as homogeneous catalysts. Some reactions exhibit autocatalysis (explain). Acid-catalyzed hydrolysis of an ester is an example of ______, where the carboxylic acid product acts as a _____ to the reaction.

Concentrations of catalysts used in a lab are typically _____ relative to the concentrations of the reactants and products. Increasing the concentration of the catalyst in such a case can ______ the rate of the reaction. When this happens, the concentration of the catalyst will be found in the ____ ____.

When the concentration of the catalyst is large relative to the reactants and products, the rate changes _____ or not at all with an increase in the catalyst concentration. In such a case, the concentration of the catalyst will likely not be included in the ____ ____. Reactions with catalysts require separate _____ _____.

Since the catalyst does not prevent the original reaction from proceeding, the total rate is given by the ____ of the rates of both reactions. For instance, a first order uncatalyzed reaction may follow the rate law:
rate = k₀[A]
When the same reaction is catalyzed by acid, what is the new rate law?
Typically, the rate of the original reaction is _______ compared to the rate of the catalyzed reaction.

Enzymes are _____ _____ that speed up almost every chemical reaction in the human body. Most enzymes are far _____ effective than the catalysts found in the lab due to their ______. The number of reactions occurring at a single active site on one enzyme is around _____ per second and can be tens of thousands of times _____ for the ______ enzymatic reactions. This number is called the ______ _____.

Roughly speaking, liquid molecules have around ____ times more collisions per second than gas molecules (why?) However, most of the collisions in a liquid are with the ______ molecules rather than _____ molecules, and thus do not lead to a _____.

The rate constant in a liquid is a function of both the _______ and the ______. Solvents can _____ ______ reactants, ______ the electrostatic forces between them. 1)The _____ of the solvent affects k, the rate constant. 2)The _____ ___ _____ also affects k.

When a reactant is dissolved in a solvent, it becomes ______, spreading out and becoming surrounded by the ______ molecules. The intermolecular interactions between solvent and reactant ______ the reactant. These solvent-reactant attractions must be overcome before a ______ can take place. The solvent may also ______ reaction intermediates.

3)Solvent viscosity affects k through the '_____ _____' (explain)

If another reactant also gets trapped in the cage, many of the collisions are between the _____ and a reaction is _____ to occur. If there is not another reactant in the solvent cage, what happens to the molecule? The net result is that reactants in a _____ collide at a rate approximately equal to the rate of collisions between reactants in a ____ with _____ concentrations.

For liquids, stirring or shaking may greatly _____ the number of collisions and thereby the _____ ____. Increasing the temperature of the liquid increases the ______ energy of the particles, which also ______ the reaction rate.

Nuclear decay involves the _____ of particles within the _____ of an atom and knowing the rate of nuclear decay is important. Recall that atomic nuclei are held together by _____ _____ _____. Without it, protons would _____ one another. Neutrons _____ _____ the protons and _____ the nucleus.

Radioactive decay concerns atoms that _______ break apart. All atoms other than _______ are subject to some type of spontaneous decay. The mass and identity of an atom is located within its ______. The rate at which decay occurs _____ _______. Atoms with a relatively high decay rate are said to be _______.

There is no way to predict precisely when an individual atom will spontaneously decay. However, atoms are small, and there are usually ______ of them in a given sample. The rules of probability apply to _____ groups of atoms, allowing for predictions about their behavior. A given sample has a predictable rate of decay, usually given in terms of a half-life (define).

Radioactive decay follows _____ _____ kinetics, and the amount of atoms that remain after decay can be expressed as follows:
A_t= A₀e(^-kt) or as shown in Figure 1.24, ln(A_t/A₀) =- kt
where At is the amount at _____ t, A0 is the ____ _____, k is the ____ _____, and t is _____. Notice that radioactive decay describes a constant (e) being raised to an exponent (kt) . As described in the context of MCAT® math, this type of relationship is exponential. In other words, radioactive decay is a type of _____ _____. Plotting the logarithm of amount of atoms as a function of time would produce a straight line ____ ____ ____

There are three types of radioactive decay on the MCAT®: _____ _____, _____ _____, and _____ _____ or the production of _____ _____. Positron emission and electron capture are types of beta decay. Remembering how each particle is written and on which side of the equation it belongs turns a decay problem on the MCAT® into a simple math problem. Make sure that the sum of the atomic numbers and the sum of the mass numbers on the left side of the equation equal the sum of the _____ numbers and the sum of the _____ numbers on the right side of the equation.

Recall that the elemental identity of an atom is defined by the number of _____. This means that a change in the number of protons, as happens in some types of radioactive decay, leads to a change in the _____ of an element. By contrast, an atom that loses or gains _____ or _____ is still the same element, an ______ or _____ respectively.

The element that remains after radioactive decay can be identified by moving _____ or _____ on the periodic table. The addition of a proton is essentially a move to the _____; the loss of a proton is a move to the _____.

Define alpha particle

Beta decay (β-decay) is the breakdown of a neutron into a ______ and ______, and the _______ of the newly created electron. Since a neutron is ______, but a proton is ______, the _____ ______ stays the same, but the _____ _____ increases by one. An example of beta decay is:

A _____ (not shown) is also emitted during beta decay. It is a virtually ______ particle. It is typically represented by the Greek letter ____.

Positron emission is the emission of a _____ when a proton becomes a _____. Positron emission is considered to be a type of ____ ____. A positron can be thought of as _____ with a _____ charge. Both electrons and positrons are considered to be ____ particles. In positron emission, a _____ is transformed into a neutron and a ______ is emitted. An example of positron emission is:

Electron capture is the capture of an electron and the merging of that electron with a _____ to create a _____. In electron capture, a proton is ______ and a _____ is created. An example of electron capture is:

A gamma ray is a _____ _____ _____. It has no _____ or _____, and does not change the identity of the atom from which it is given off. Gamma decay (y decay), or gamma ray emission, often ______ the other types of radioactive decay. Gamma ray emission can occur when an _____ and _____ collide. This is a _____-_____ collision called ______. Mass is ______, converted to _____ in the form of gamma rays.

State the symbols of the following particles

State the process, change in mass #, change in atomic #, as well as the new element name of the following types of decay