* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 16 Handout
Van der Waals equation wikipedia , lookup
Statistical mechanics wikipedia , lookup
Thermodynamic equilibrium wikipedia , lookup
Vapor–liquid equilibrium wikipedia , lookup
Acid dissociation constant wikipedia , lookup
Thermodynamics wikipedia , lookup
Detailed balance wikipedia , lookup
Acid–base reaction wikipedia , lookup
Ultraviolet–visible spectroscopy wikipedia , lookup
Electrochemistry wikipedia , lookup
Woodward–Hoffmann rules wikipedia , lookup
Supramolecular catalysis wikipedia , lookup
Marcus theory wikipedia , lookup
Physical organic chemistry wikipedia , lookup
Stability constants of complexes wikipedia , lookup
Ene reaction wikipedia , lookup
Enzyme catalysis wikipedia , lookup
Industrial catalysts wikipedia , lookup
Hydrogen-bond catalysis wikipedia , lookup
Chemical thermodynamics wikipedia , lookup
Reaction progress kinetic analysis wikipedia , lookup
George S. Hammond wikipedia , lookup
Rate equation wikipedia , lookup
Determination of equilibrium constants wikipedia , lookup
Equilibrium chemistry wikipedia , lookup
Chapter 16 – Controlling the Yield of Reactions The stage when the quantities of reactants and products remains unchanged is called the chemical ____________________. Reaction yield is the extent of conversion of reactants into products, or how far the reaction will go. Some ____________________. and chemical changes can be reversed. For example ice to liquid water and back again. A double arrow ____________________.) is used to indicate a ____________________. reaction. We can use the idea that processes can be reversed to understand why some reactions reach an ____________________.. Chemists have shown that in these reactions the forward and reverse reactions occur ____________________.. For example, nitrogen gas and hydrogen gas were added to a sealed container at a constant temperature. The nitrogen and hydrogen start to react immediately, forming ammonia. The following sequence of events then occurs: –As the ____________________. reaction proceeds, the concentration of nitrogen and hydrogen decrease, so the rate of ammonia production decreases. –At the same time the ammonia is being formed, some ammonia molecules react to re-form nitrogen and hydrogen. The rate of this ____________________. reaction increases as the concentration of ammonia increases. –Eventually the ____________________. and back reactions proceed at the same ____________________.. When this situation is reached, the ammonia is formed at exactly the same rate it is breaking down. –The ____________________. of the hydrogen, nitrogen and ammonia will remain constant. –At the ____________________. position no further change will take place in the rate of either the forward or back reaction. The reaction has reached a point of ____________________., an equilibrium. Draw an example of the establishment of equilibrium Equilibrium is a ____________________. state, since the forward and back reactions have not ceased. They occur simultaneously at the same rate. During dynamic equilibrium: –The ____________________. and concentrations of chemical substances remain constant. –The total gas ____________________. is constant (if gases are involved) –The ____________________. us constant –The reaction is ____________________. (all of the substances are present in the equilibrium mixture). Different reactions proceed to ____________________. extents. For example a ____________________. acid, like HCl, almost completely ionises. Whereas a ____________________. acid, like ethanoic acid, does not completely ionise. This is shown by their electrical conductivity. As such their point of ____________________. is different. K is known as the ____________________. constant. K can be found by finding the concentration fraction, also known as the reaction quotient. While the concentration fraction can be ____________________. for any mixture of reactants and products, it is only at equilibrium that it has a constant value. K = [products] [reactants] From studies of equilibria, chemists have found that: –Different chemical reactions have ____________________. values of K –For a particular reaction, K is constant for all equilibrium mixtures at a fixed ____________________.. The equilibrium constant gives us an indication of the extent of the reaction. For values of K that are between 10-4 and104, there will be significant amounts of reactants and products present at equilibrium. For values of K that are ____________________. (>104), the equilibrium mixture consists mostly of ____________________. with small amounts of reactants. For values of K that are ____________________. (<10-4) the equilibrium mixture will consist mostly of ____________________. with small amounts of products. The value of K, for a particular reaction, depends only on ____________________.. It is not affected by addition of reactants or products, changes in pressure or the use of catalysts. As temperature increases: –For ____________________. reaction, the amount of products decreases so the value of K ____________________.. –For ____________________. reactions, the amount of products increases and so the value of K ____________________.. The equilibrium position of a reaction may be changed by: –____________________. or removing a reactant or product –Changing the ____________________. by changing the volume (equilibria involving gases) –____________________. (for equilibria in solution) –Changing the ____________________ Suppose a vessel contains an equilibrium mixture represented by the equation: ________________________________________________________________________ If extra nitrogen gas were added to the vessel without changing the volume or temperature, the mixture would momentarily not be in equilibrium. The following events occur as the composition of the mixture adjusts to return to the equilibrium: –The ____________________concentration of nitrogen gas causes the rate of the forward reaction to increase and more ammonia is formed. –As the ____________________of the ammonia increases, the rate of the back reaction to reform N2 and H2 increases. –Ultimately the rates of the forward and back reaction become equal again and a new ____________________is established. When equilibrium is re-established the concentration of all substances have changed. The overall effect of ____________________nitrogen is to increase the concentration of ammonia at equilibrium – a net forward reaction. Addition of more NH3, increases the rate of the back reaction. To summarise: –____________________of a reactant leads to the formation of more products (a net ____________________reaction). –Addition of a ____________________leads to the formation of more reactants (a net ____________________reaction). Le ____________________Principle: if an equilibrium system is subjected to a change, the system will adjust itself to partially oppose the effect of the change. The ____________________of gases in an equilibrium mixture can be changed by increasing or decreasing the ____________________of the container while keeping the temperature constant. In general the effect of a change in ____________________, by changing the container volume, depends on the relative ____________________of gas particles on both sides of the equation. The total ____________________of an equilibrium mixture of gases may also be changed by adding a non-reacting gas such as helium, neon or argon. Despite the increase in total pressure that occurs when this gas is added, the concentration of the individual chemicals involved in the equilibrium are not affected by the presence of the extra gas. The system therefore stays in ____________________and there is no net ____________________or back reaction. The effect of ____________________a solution by adding water is similar to changing the volume in gaseous equilibria. Where possible, a net reaction occurs in the direction that produces the greater ____________________of particles. For example, dilution of a solution containing the equilibrium system: Fe3+(aq) + SCN-(aq) 2 particles in solN Fe(SCN)2+(aq) 1 particle in solN Results in an ____________________in the amount of Fe3+ and SCN- ions. In terms of Le Chatelier’s principle, a net back reaction increases the total concentration of particles in solution, offsetting the effect of dilution. Despite the net back reaction, the concentration of Fe3+ and SCN- at the new ____________________will be lower than their concentration prior to the dilution as the equilibrium shift partially offsets the change. ____________________increases the energy of the substances in the mixture. Applying Le Chatelier’s Principle to an ____________________reaction, the reaction opposes an increase in energy by removing energy – that is a net ____________________reaction occurs. For an ____________________reaction, net forwards reactions occur as the temperature rises. An ____________________in temperature in an equilibrium mixture reaction results in: –A net ____________________reaction (less products) for exothermic reactions –A net ____________________reaction (more products) for endothermic reactions. ____________________increase the rate of reactions. It has been shown that they increase the rate of forward and back reactions equally. As a consequence, the presence of catalyst does not change the ____________________of equilibrium. A catalyst may greatly ____________________the rate at which equilibrium is reached. Many reactions can be regarded as continuing until they are complete. These include: –Reactions that produce ____________________such as gases that escape from the reaction mixture as they are formed. Continual loss of products drives these reactions ____________________. –Reactions that form ____________________in which only minute quantities of reactants are present. Reactants Products Add reactants: Add products: Increase pressure: Eg 2 reactant particles particle 1 product Eg 1 reactant particle 2 product particles Increase temperature: Exothermic reactions Endothermic reactions Add a catalyst: Does not alter the extent of a reaction