How to distinguish between a zero order reaction, a first order reaction, and a second order reactio

1. Zero-level reaction.

Definition: Reaction rate.

What is not related to the concentration of a substance is called a zeroth order reaction.

There are not many reactions with a total order of zero reactions, and the most known zero-order reactions are surface catalytic reactions. For example, ammonia in tungsten metal.

on the decomposition reaction.

Since the reaction takes place only on the surface of the catalyst, the reaction rate is only related to the surface state. If the metal surface has been saturated with adsorbed NH3, increasing the concentration of NH3 will no longer affect the reaction rate, and the reaction will be a zero-order reaction to NH3.

2. First-level reaction.

Definition: Any reaction rate that is only proportional to the concentration of a substance is called a first-order reaction.

Nitrous pentoxide.

Decomposition reaction:

The rate equation for the reaction is:

It can be seen that this reaction is a first-order reaction.

To make a definite integral to the above equation, <

where c0 is the initial concentration and c is the concentration at the time of the reaction to t.

From this, it can be seen that when half of the reactants are consumed, there is <>

It can be seen that the half-life of the primary reaction.

and the rate constant of the reaction.

k is inversely proportional and independent of the initial concentration of the reactants, which is also a characteristic of the first-order reaction.

3. Secondary reaction.

Definition: The rate of reaction and the concentration of a substance to the power of the power.

The proportional one is called the second order reaction.

Its velocity equation:

Therefore, it is a grade 1 reaction to CO; is a grade 1 response to NO2; This reaction is a second-order reaction. Dimension of the 2nd order reaction k.

mol-1·dm3·s-1。

Zero-order reaction The rate of zero-order reaction is independent of the concentration of reactants, but is affected by other factors, such as the solubility of reactants, or the illuminance of light in some actinic reactions. The rate equation for the zero-order reaction is: (12-2) Integral:

C=C0 - K0 t (12-3), where C0-T=0 reactant concentration, mol l; Concentration of reactants at c-t, mol l; k0 - the zero-order rate constant, which is linearly related to t, the slope of the straight line is -k0, and the intercept is c0. Secondary Reaction The reaction speed is proportional to the product of the concentrations of the two reactants, that is, a chemical reaction that is proportional to the second quadratic of the concentration of the reactants is called a secondary reaction. The equation for the reaction velocity of the second-order reaction is:

dx dt=k(a-x(b-x) A and b are the concentrations at the beginning of the reactants, and x is the concentration of the product. If a b then dx dt=k(a-x)(a-x) is plotted with 1 a-x against t, and the line is straight. This is characteristic of secondary reactions.

The half-life of the second-order reaction is 1 ka, that is, the larger the concentration of reactants at the beginning, the shorter the time required to complete the halving of the concentration First-order reaction The rate of the first-order reaction is proportional to the primary square of the concentration of reactants, and its rate equation is: (12-4) The relationship between concentration and time after integration: (12-5) where k-first-order rate constant, s-1, min-1 or h-1, d-1, etc.

The slope of the straight line is -k and the intercept is LGC0. Usually, the time required for half of the reactants to be consumed is half life, which is denoted as T1 2, and at constant temperature, the T1 2 of the primary reaction is independent of the reactant concentration. (12-6) For drug degradation, the time required for 10% degradation is commonly used, called one-tenth of the life, which is recorded as constant temperature, and has nothing to do with the concentration of reactants.

12-7) A reaction in which the reaction rate is proportional to the product of the concentrations of the two reactants is called a secondary reaction. If the concentration of one of the reactants greatly exceeds that of the other, or if the concentration of one of the reactants is kept constant, the reaction shows the characteristics of a first-order reaction, so it is called a pseudo-first-order reaction. For example, the hydrolysis of esters, catalyzed by acids or bases, can be treated as a pseudo-first-order reaction.

First, the nature is different.

1. Zero-order reaction: a chemical reaction in which the reaction rate is proportional to the zero power of the reactant concentration (that is, it has nothing to do with the reactant concentration).

2. First-order reaction: It is a reaction in which the reaction speed is only proportional to the primary square of the concentration of reactants.

Second, the reaction equation is different.

1. Zero-order reaction: if for any zero-order reaction: a(g)-product, then d[a] dt=k0 [a]0 = k0, that is, d[a]= -k0dt, when t=0, [a]=[a]0, when the time is t, [a]=[a]t, both sides integrate, collated, [a]t=[a]0-k0t.

2. First-order reaction: its reaction velocity equation can be expressed as: differential form:

r = -dc dt = kc integration form: ln(a c) = kt. In the above formula, a is the concentration of reactants at the beginning of the reaction, c is the concentration of reactants at time t, k is the rate constant, and the unit is the negative primary square of the time unit, such as s-1, min-1 or h-1, d-1, etc.

In chemical kinetics, zero-order reactions, first-order reactions, and second-order reactions can be distinguished by observing the reaction rate as a function of reactant concentrations.

1.Zero-order reactions: Zero-order reactions are reactions in which the reaction rate is independent of the concentration of reactants.

In a zero-order reaction, the reaction rate is constant and is not affected by the concentration of reactants. Graphically, the concentration of reactants in the zero-order reaction decreases linearly with time. For example, the autocatalytic decomposition of a substance in solution is a zero-order reaction.

2.Primary reaction: A primary reaction is a reaction in which the rate of reaction is proportional to the concentration of one reactant.

In a primary reaction, the reaction rate slows down as the concentration of reactants decreases. Graphically, the concentration of reactants in the primary reaction decreases exponentially with time. For example, radioactive decay, reactions catalyzed by certain enzymes, etc., are all first-order reactions.

3.Secondary reaction: A secondary reaction refers to a squared relationship in which the rate of the reaction is proportional to the concentration of one or two reactants.

In a secondary reaction, when the concentration of either or both reactants decreases, the reaction rate decreases significantly. Graphically, the concentration of reactants in the secondary reaction decreases by square root over time. For example, certain intermolecular reactions, certain enzyme-catalyzed reactions, etc., are secondary reactions.

The level of the reaction can be determined by experimentally measuring the reaction rate as a function of the reactant concentration. It is important to note that some reactions may have multiple levels at the same time, in which case more complex kinetic models are required to describe.

To distinguish between zero-order reactions, first-order reactions, and second-order reactions, it can be judged according to the relationship between the reaction rate and the concentration of reactants. The following are the characteristics and judgment methods of the reactions at all levels:

Zero-order reaction: Feature: The reaction rate is independent of the reactant concentration, that is, the reaction rate is constant. Judgment method: Draw an image of the concentration and time of the reactants, if it is a straight line, it is a zero-order reaction.

Primary Reaction: Feature: The reaction rate is proportional to the reactant concentration, i.e., the reaction rate slows down as the reactant concentration decreases. Judgment method: Draw an image of the concentration and time of the reactants, if it is an exponential decay curve, it is a first-order reaction.

Secondary Reaction: Features: The reaction rate is proportional to the square of the reactant concentration, i.e., the reaction rate slows down rapidly as the reactant concentration decreases.

Judgment method: Draw an image of the concentration and time of the reactants, if it is an exponential growth curve, it is a secondary reaction.

It should be noted that the above judgment method is based on the relationship between the reaction rate and the concentration of reactants, and other factors need to be considered in the actual judgment, such as reaction mechanism and reaction kinetics. Therefore, the most accurate way to determine this is to determine the reaction rate constant experimentally and perform a kinetic analysis.

The rate of the zero-order reaction is constant, and if the half-life is t, the complete reaction takes 2t

The rate of the first-order reaction is proportional to the concentration of reactants, and the half-life is independent of the initial concentration, if the half-life is t, the quarter life is 2t

The rate of the secondary reaction is proportional to the square of the reactant concentration, and the half-life is inversely proportional to the initial concentration, if the half-life is t, then the quarter life is (t+2t).

Zero-order reactions, first-order reactions, and trace-second reactions are different types of the relationship between the rate of chemical reaction and the concentration of reactants.

1.Zero-order reaction characteristics:

The zero-order reaction rate is independent of the reactant concentration, i.e., the reaction rate is constant.

When the reactant concentration decreases, the reaction rate is not affected.

During a zero-order reaction, the reactants are consumed at a fixed rate.

2.Primary Reaction Characteristics:

The first-order reaction rate is directly proportional to the concentration of reactants, that is, the rate and concentration are linear.

When the concentration of reactants decreases, the reaction rate decreases accordingly.

In the primary reaction, the half-life of the reactants is constant, i.e., the same amount of time is required to reduce the reactant concentration by half.

3.Secondary Reaction Characteristics:

The rate of the secondary reaction is proportional to the square of the concentration of the reactants, that is, the square of the rate and the concentration is linear.

When the concentration of reactants decreases, the reaction rate decreases more quickly.

In the secondary reaction, the half-life of the reactants is concentration-dependent, that is, when the concentration is higher, the half-life is shorter.

It is important to note that these features are models built under ideal conditions, and actual responses are often influenced by other factors that may deviate from these features.

First-order reaction: defeat is the rate of reaction.

The one that is proportional only to the concentration of the substance once is called a first-order reaction.

Secondary reaction: the ratic of the reaction rate and the concentration of the substance.

The proportional one is called the second-order reaction.

Zero-order reaction: The reaction rate is not related to the concentration of the substance is called the zero-order reaction.

Rate constant. The unit is a unit of time.

of the negative primary square, such as s-1, min-1 or h-1, d-1, etc.

ln(a c) has a linear relationship with time.

Half-life. is a constant independent of the initial concentration, i.e., t1 2=.

First-order reaction: defeat is the rate of reaction.

The one that is proportional only to the concentration of the substance once is called a first-order reaction.

Secondary reaction: the ratic of the reaction rate and the concentration of the substance.

The proportional one is called the second-order reaction.

Zero-order reaction: The reaction rate is not related to the concentration of the substance is called the zero-order reaction.

Rate constant. The unit is a unit of time.

of the negative primary square, such as s-1, min-1 or h-1, d-1, etc.

ln(a c) has a linear relationship with time.

Half-life. is a constant independent of the initial concentration, i.e., t1 2=.

First-order reaction, meaning its reaction rate.

It is only proportional to the first square of the concentration of the substance, and the English is first order reaction.

The second-order reaction means that its reaction rate and concentration of the substance are defeated to the second power.

Proportional, English is second order reaction.

Zero-order reaction, which means that its reaction rate is independent of the concentration of the substance, is called zero-order reaction, which is zeroth order reaction in English.

A zero-order reaction is a reaction classified in terms of chemical reaction rate, which is a reaction in which the reaction rate does not change with the change of concentration, or a reaction that is proportional to the zero power of the concentration (n-order is proportional to the n-level of the concentration). It is generally a photochemical reaction.

Primitive reaction refers to the reaction in which the reactant molecule is directly converted into a product in one step, and the reaction order is related to its reaction rate equation.

Primitive reactions can be primary, secondary, or zero-order, and there is no direct correlation between the two, e.g. if there is a primitive reaction AA

bb==gg+hh

The equation for its velocity is.

kc(a)^a

c(b)^b

Then the reaction order is (a+b).

A zero-order reaction is a reaction with a constant reaction rate, which always proceeds at this rate.