File Name: rate of chemical reaction and chemical equilibrium .zip
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The equilibrium of a reaction mixture is characterized by the fact that at a certain temperature, the concentrations or the pressures of the reactants and products in a given ratio are constant expressed by the equilibrium constant. The theoretical analysis of chemical equilibria is the subject of thermodynamics. Chemical reactions that are far of a thermodynamic equilibrium, are, for example, the oscillating reactions.
Chemical Equilibrium Pdf
Chemistry: Equilibrium and Advanced Thermodynamics Transcript. Light a match and chemical change happens in a one-way process: Reactants are transformed into products. Some chemical reactions happen spontaneously, like metal rusting. Other reactions are non-spontaneous and need to absorb energy in order to occur. Using the Second Law of Thermodynamics, the principle of entropy, and the calculation of Gibbs free energy, scientists can predict which reactions will occur and vary the conditions to make more of the desired products.
In equilibrium reactions, both products and reactants are always present. Equilibrium reactions in the human body are essential for life and can be exploited in chemical manufacturing as well. In Unit 7, we discussed thermochemistry the study of energy in chemical reactions , the First Law of Thermodynamics the conservation of energy , and exothermic and endothermic reactions how chemical reactions release or absorb energy.
Another goal of thermodynamics is to understand why some reactions occur and others do not. Figure Spontaneous Reactions Two examples of spontaneous processes: ice melting at room temperature and iron rusting.
A spontaneous process happens without any outside intervention or input of energy. For example, liquids freeze spontaneously at temperatures below their freezing points. Salt spontaneously dissolves in warm water, and will not spontaneously recrystallize.
A ball spontaneously rolls downhill and loses energy as it goes. A ball does not spontaneously roll uphill; pushing it back uphill requires an input of energy. Many chemical reactions follow the same pattern as that ball. Burning glucose is spontaneous and releases energy:. The reverse reaction is nonspontaneous and requires an input of energy. In photosynthesis, plants reverse this reaction to create glucose; the energy input comes from sunlight.
It may be tempting, then, to assume that exothermic processes are always spontaneous, and endothermic reactions are nonspontaneous. While this is often true, there are many examples that run counter to this trend. Table salt dissolves spontaneously in water, for instance, and yet this process is endothermic.
Clearly, there is more to spontaneity than energy. In , Austrian physicist Ludwig Boltzmann — published the key research that explained spontaneity. Because the numbers of particles involved in chemical reactions are astronomically large, Boltzmann used statistics to describe the positions and energies of the particles.
Thus, Boltzmann is the founder of statistical mechanics , an approach that revolutionized the study of thermodynamics. Two-Bulb Apparatus When the valve between the two bulbs opens, the gas particles distribute themselves evenly throughout because an even distribution is statistically most likely. Rather than trying to follow every particle in a reaction at the same time, he just looked at the chances of where the particles were likely to be, and from that, thermodynamics could be explained.
Consider the two-bulb apparatus shown in Figure Two glass bulbs connect to each other through a valve. In the top portion of the image, the valve is closed, and the bulb on the left contains a quantity of purple gas; the bulb on the right is empty. Opening the valve allows the gas to travel into the other bulb until the amounts of gas are equal on each side; this process is spontaneous. The reverse process, where the gas gathers together on one side of the apparatus, is nonspontaneous. The atoms can be in one of 16 possible arrangements at any given time.
Figure At any particular point in time, the atoms will be in one of 16 possible arrangements. Each one of these arrangements, such as having all the atoms on the left and none on the right, or having the red, yellow, and blue atoms on the left and the green on the right, is called a microstate. The microstate is a specific description of where the particles are. Counting up the number of atoms on each side gives us the macrostate. The macrostate describes the overall distribution of the atoms, for example, four atoms on the left and zero on the right , or three atoms on the left and one on the right Table shows all the possible microstates and macrostates for this experiment.
With four particles, there are 16 possible microstates divided into five possible macrostates. The most common macrostate is the distribution; because of the 16 possible microstates, six will create this macrostate. Four microstates make up the and macrostates, making those less likely to occur.
Much less likely to occur are the or macrostates, because only one in 16 microstates create them. Even though the atoms are moving randomly, and even though no microstate is more likely than any other, the results show that the most likely macrostate is an equal distribution with two atoms on each side.
The more entropy a macrostate has, the more likely that macrostate is to occur. In more general terms though, entropy is really a measure of the system disorder; the more particles we have, the more possible arrangements we have, and essentially the more mess we can make.
Imagine a bedroom: Take out all the clothes and put them on the floor. The more clothes we own, the more of a disordered mess the floor of the room will be.
The same is true of molecules. The distribution of gas particles is just one way to see the effects of entropy. As we will see in the next section, entropy determines not only how particles arrange themselves in space, but also how heat flows between objects.
In the previous section, we saw how the random movement of gas particles leads to an even distribution of those particles inside a container. In other words, the spread-out macrostate has the most entropy. Energy Quanta Like particles of gas, energy quanta also distribute themselves according to statistical mechanics. A similar analysis explains why heat flows from hot objects to cold objects. When two objects of different temperature are brought into contact, the quanta of energy distribute themselves uniformly throughout just like gas particles spreading throughout their container.
Just as the most probable macrostate for the gas particles was , the most probable macrostate for the energy quanta is As noted in the introduction to this unit, exothermic reactions are often but not always spontaneous.
The underlying reason for this is that exothermic reactions increase entropy by releasing quanta of energy. The quanta spread out, and entropy increases. Thus, exothermic reactions tend to be spontaneous. Energy quanta can spread by transferring from one particle to another throughout an object, but they can also spread out in a different sense.
Not only can a quantum jump between particles, but it can also cause the particle to move in different ways. Figure A quantum of energy might make a particle move through space faster; this is called translational energy. It also might cause a molecule to rotate in place; this is called rotational energy. Finally, a quantum of energy might cause the bonds of a molecule to vibrate. Energies Energy can cause a molecule to move in different ways: vibration of its bonds, rotation of the molecule as a whole, or translation movement through space.
The more ways a molecule can move, the more ways quanta of energy can be distributed. The water molecules in an ice cube can only vibrate in place. Quanta of energy are restricted to vibrational energy, and therefore ice has a low entropy value. In liquid water, the quanta can spread out to cause vibration and rotation; liquid water has higher entropy. Gaseous water steam has the highest amount of entropy because the molecules possess vibrational, rotational, and translational energies.
In the previous sections, we saw that high entropy is associated with two things: a wide distribution of particles and a wide distribution of energy quanta. The more particles and energy quanta can spread out, the more entropy there is.
Bearing this in mind, it should make sense that a substance in the solid phase would have relatively low entropy. In a solid, the particles are locked in place and highly ordered, the clear opposite of disorder or entropy.
The quanta of energy in a solid are restricted mainly to vibration, so the distribution of quanta is also minimized. Entropy and the States of Matter Entropy increases as temperature increases and as a substance changes from solid to liquid to gas. The entropy of the liquid phase is higher. The particles are no longer locked in place. Because they are now free to move, they can distribute themselves in more ways.
The energy quanta can distribute themselves in a greater variety of ways as well. Like a solid, the molecules can vibrate; but because they have more freedom of movement, molecules have rotational and some translational energy, too. Gases have the highest entropy values because they have the greatest freedom of movement. Gas particles are separate and distribute themselves throughout their container see Section 2: Microstates, Macrostates, and Matter. And, gases also possess all three types of energy: translational, rotational, and vibrational.
Finally, a substance that is dissolved in a liquid also has a high level of entropy for reasons similar to gases. Dissolved particles are free to not only move throughout the volume of the liquid, but also to move in all three ways.
Generally speaking, the entropy value of a dissolved substance is higher than pure liquids but less than gases. To summarize, the entropy of the phases of matter are:. Using this information, we can make an educated guess about whether entropy is increasing or decreasing when a chemical reaction occurs. Consider the following reaction in which solid table salt dissolves in water:. In this case, a solid low entropy is turning into two aqueous ions higher entropy. We can reasonably assume that entropy increases.
As we know, this reaction is spontaneous; salt dissolves in water. Consider another spontaneous process, the sublimation of dry ice solid CO 2 :. Both of the above reactions are spontaneous, and both produce products with higher entropy than the reactants.
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Chemical kinetics , also known as reaction kinetics , is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is to be contrasted with thermodynamics, which deals with the direction in which a process occurs but in itself tells nothing about its rate. Chemical kinetics includes investigations of how experimental conditions influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition states , as well as the construction of mathematical models that also can describe the characteristics of a chemical reaction. In , Peter Waage and Cato Guldberg pioneered the development of chemical kinetics by formulating the law of mass action , which states that the speed of a chemical reaction is proportional to the quantity of the reacting substances. Relatively simple rate laws exist for zero order reactions for which reaction rates are independent of concentration , first order reactions , and second order reactions , and can be derived for others. Elementary reactions follow the law of mass action , but the rate law of stepwise reactions has to be derived by combining the rate laws of the various elementary steps, and can become rather complex. In consecutive reactions, the rate-determining step often determines the kinetics.
Chemistry: Equilibrium and Advanced Thermodynamics Transcript. Light a match and chemical change happens in a one-way process: Reactants are transformed into products. Some chemical reactions happen spontaneously, like metal rusting. Other reactions are non-spontaneous and need to absorb energy in order to occur. Using the Second Law of Thermodynamics, the principle of entropy, and the calculation of Gibbs free energy, scientists can predict which reactions will occur and vary the conditions to make more of the desired products. In equilibrium reactions, both products and reactants are always present. Equilibrium reactions in the human body are essential for life and can be exploited in chemical manufacturing as well.
2.5: Reaction Rate
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The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium , a state approached by a dynamic chemical system after sufficient time has elapsed at which its composition has no measurable tendency towards further change. For a given set of reaction conditions, the equilibrium constant is independent of the initial analytical concentrations of the reactant and product species in the mixture. Thus, given the initial composition of a system, known equilibrium constant values can be used to determine the composition of the system at equilibrium. However, reaction parameters like temperature, solvent, and ionic strength may all influence the value of the equilibrium constant.
The Effect of a Catalyst on Equilibrium
In this page find chemical reactions and equations class 10 worksheet with answers. Covers how rate of reaction can be measured, collision theory, catalysts, reversible reactions, equilibrium, and the effect of changing conditions on position of equilibrium and The Midterm will have material not on the midterm recap! Unit 5 Review Activity. A reaction is found to be second order in carbon monoxide concentration. What happens to the rate of the reaction if the [CO] is doubled, with everything else kept the same. Write the equation for the rate law below.
Chemical equilibrium , a condition in the course of a reversible chemical reaction in which no net change in the amounts of reactants and products occurs. A reversible chemical reaction is one in which the products, as soon as they are formed, react to produce the original reactants. At equilibrium , the two opposing reactions go on at equal rates, or velocities , hence there is no net change in the amounts of substances involved. At this point the reaction may be considered to be completed; i. The conditions that pertain to equilibrium may be given quantitative formulation.
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Chemical Equilibrium Pdf MINTEQA2 is a equilibrium speciation model that can be used to calculate the equilibrium composition of dilute aqueous solutions in the laboratory or in natural aqueous systems. Chemical Kinetics Reaction Rates Part 1. Chemical Equilibrium Questions and Answers Study. The model is useful for calculating the equilibrium mass distribution among dissolved species, adsorbed species, and multiple solid phases under a variety of conditions.
PCL5is kept in a closed container at a temperature of K the equilibrium concentration of the … Equilibria are those in which the reactants and products are present in more than phases: Physical. Chemical equilibrium refers to the state of a system in which the concentration of the reactant and the concentration of the products do not change with time and the system does not display any further change in properties. Equilibrium can be attained from either side.
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