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The following reaction, catalyzed by iridium, is endothermic at \(700 \mathrm{~K}\) : $$ \mathrm{CaO}(s)+\mathrm{CH}_{4}(g)+2 \mathrm{H}_{2} \mathrm{O}(g) \rightleftharpoons \mathrm{CaCO}_{3}(s)+4 \mathrm{H}_{2}(g) $$ For a reaction mixture at equilibrium at \(700 \mathrm{~K}\), how would the following changes affect the total quantity of \(\mathrm{CaCO}_{3}\) in the reaction mixture once equilibrium is re-established? (a) Increasing the temperature (b) Adding calcium oxide (c) Removing methane \(\left(\mathrm{CH}_{4}\right)\) (d) Increasing the total volume (e) Adding iridium

Short Answer

Expert verified
(a) Increase, (b) Increase, (c) Decrease, (d) Increase, (e) No change

Step by step solution

01

Analyze the Reaction and Le Chatelier's Principle

The reaction is endothermic at 700 K, meaning that the forward reaction absorbs heat. According to Le Chatelier's principle, the system will adjust to minimize the effect of any changes to the equilibrium conditions. This principle will guide us in predicting the effect of different changes on the equilibrium position and the total quantity of CaCO₃.
02

Effect of Increasing the Temperature (a)

Increasing the temperature of an endothermic reaction shifts the equilibrium towards the products to absorb the extra heat. Thus, increasing the temperature will increase the amount of CaCO₃ formed.
03

Effect of Adding Calcium Oxide (b)

Adding more CaO will cause the reaction to favor the forward reaction to consume the added reactant. Hence, the total quantity of CaCO₃ will increase as the equilibrium shifts to the right.
04

Effect of Removing Methane (c)

Removing CH₄ reduces the concentration of the reactants, causing the equilibrium to shift to the left toward the reactants to compensate. This shift decreases the amount of CaCO₃.
05

Effect of Increasing the Total Volume (d)

Increasing the total volume reduces the pressure. Since this reaction involves more gas molecules on the product side (4 H₂) than on the reactant side (3 total gases), the equilibrium will shift to the side with more gas particles. Therefore, increasing the total volume will increase the amount of CaCO₃ formed.
06

Effect of Adding Iridium (e)

Iridium acts as a catalyst in the reaction, which increases the rate of both the forward and reverse reactions equally without affecting the equilibrium position. Therefore, adding iridium does not change the equilibrium concentration of CaCO₃.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Endothermic Reaction
In an endothermic reaction, the system absorbs heat from its surroundings. This absorption of heat is a key feature of endothermic processes and affects how the equilibrium changes when conditions like temperature shift. Le Chatelier's Principle helps to predict these changes. If the temperature increases, the reaction shifts towards the products to absorb the added heat. This is because an endothermic reaction requires heat as an input, and adding heat effectively supplies more of a reactant. Thus, in the given reaction at 700 K, increasing the temperature means more calcium carbonate \(CaCO_3\) will be produced as the system shifts to the right to counteract the increase in temperature.
Chemical Equilibrium
Chemical equilibrium occurs when the forward and reverse reactions proceed at the same rate. At equilibrium, the concentrations of reactants and products remain constant over time, even though individual molecules may continue to react. Le Chatelier's Principle provides a way to predict the system's response to changes in conditions, like concentration, pressure, and temperature. For example, in the reaction given, adding more \(CaO\) would cause the equilibrium to shift towards the products. This is to consume the added reactant and re-establish equilibrium by producing more \(CaCO_3\). Conversely, removing a reactant like \(CH_4\) will shift the equilibrium toward the reactants to balance the disturbance, decreasing the amount of \(CaCO_3\). Understanding these shifts is crucial in controlling reactions in industrial applications and laboratory settings.
Catalysis
Catalysis involves the use of a catalyst, a substance that speeds up a chemical reaction without being consumed in the process. In the given reaction, iridium acts as a catalyst. A catalyst works by lowering the activation energy, making it easier for the reaction to proceed. This results in the increase of reaction rates for both forward and reverse reactions. However, a catalyst does not change the position of equilibrium. Iridium catalyzing the reaction does not alter the amount of \(CaCO_3\) at equilibrium. It merely allows the reaction to achieve equilibrium faster, which can be particularly useful in processes requiring quick turnover or where time is a limiting factor.
Reaction Kinetics
Reaction kinetics is the study of rates of chemical processes and the factors that affect them. In the reaction, kinetics involves understanding how changes in temperature, concentration, or pressure can impact the speed at which equilibrium is achieved. One principle aspect of reaction kinetics is how volume affects pressure in reactions involving gases. For the given reaction, increasing the volume decreases the pressure. Since there are more gas molecules on the product side (4 \(H_2\)) compared to the reactants (3 molecules total), Le Chatelier's Principle predicts a shift towards the products to restore equilibrium, increasing the amount of \(CaCO_3\) as a result. Overall, understanding reaction kinetics helps predict the behavior of different reactions under varying conditions, which is essential in fields like chemical engineering and environmental science.

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Most popular questions from this chapter

Acetic acid tends to form dimers, \(\left(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\right)_{2}\), because of hydrogen bonding: The equilibrium constant \(K_{c}\) for this reaction is \(1.51 \times 10^{2}\) in benzene solution, but only \(3.7 \times 10^{-2}\) in water solution. (a) Calculate the ratio of dimers to monomers for \(0.100 \mathrm{M}\) acetic acid in benzene. (b) Calculate the ratio of dimers to monomers for \(0.100 \mathrm{M}\) acetic acid in water. (c) Why is \(K_{c}\) for the water solution so much smaller than \(K_{c}\) for the benzene solution?

The first step in the industrial synthesis of hydrogen is the reaction of steam and methane to give synthesis gas, a mixture of carbon monoxide and hydrogen: \(\mathrm{H}_{2} \mathrm{O}(g)+\mathrm{CH}_{4}(g) \rightleftharpoons \mathrm{CO}(g)+3 \mathrm{H}_{2}(g) \quad K_{c}=4.7\) at \(1400 \mathrm{~K}\) A mixture of reactants and products at \(1400 \mathrm{~K}\) contains \(0.035\) \(\mathrm{M} \mathrm{H}_{2} \mathrm{O}, 0.050 \mathrm{M} \mathrm{CH}_{4}, 0.15 \mathrm{M} \mathrm{CO}\), and \(0.20 \mathrm{M} \mathrm{H}_{2}\). In which di- rection does the reaction proceed to reach equilibrium?

A chemical engineer is studying reactions to produce \(\mathrm{SO}_{3}\) as a step in the manufacture of sulfuric acid. The value of \(K_{\mathrm{p}}\) for the reaction \(2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) \rightleftharpoons 2 \mathrm{SO}_{3}(g)\) is \(2.5 \times 10^{10}\) at \(500 \mathrm{~K}\). Will a mixture of \(\mathrm{SO}_{2}\) and \(\mathrm{O}_{2}\) produce much \(\mathrm{SO}_{3}\) when equilibrium is reached?

An equilibrium mixture of \(\mathrm{PCl}_{5}, \mathrm{PCl}_{3}\), and \(\mathrm{Cl}_{2}\) at a certain temperature contains \(8.3 \times 10^{-3} \mathrm{M} \mathrm{PCl}_{5}, 1.5 \times 10^{-2} \mathrm{M} \mathrm{PCl}_{3}\) and \(3.2 \times 10^{-2} \mathrm{M} \mathrm{Cl}_{2} .\) Calculate the equilibrium constant \(K_{c}\) for the reaction \(\mathrm{PCl}_{5}(g) \rightleftharpoons \mathrm{PCl}_{3}(g)+\mathrm{Cl}_{2}(g) .\)

Halogen lamps are ordinary tungsten filament lamps in which the lamp bulb contains a small amount of a halogen (often bromine). At the high temperatures of the lamp, the halogens dissociate and exist as single atoms. (a) In an ordinary tungsten lamp, the hot tungsten filament is constantly evaporating and the tungsten condenses on the relatively cool walls of the bulb. In a Br-containing halogen lamp, the tungsten reacts with the \(\mathrm{Br}\) atoms to give gaseous \(\mathrm{WBr}_{4}:\) $$ \mathrm{W}(s)+4 \mathrm{Br}(g) \rightleftharpoons \mathrm{WBr}_{4}(g) $$ At the walls of the lamp, where the temperature is about \(900 \mathrm{~K}\), this reaction has an equilibrium constant \(K_{\mathrm{p}}\) of about \(100 .\) If the equilibrium pressure of \(\mathrm{Br}(g)\) is \(0.010 \mathrm{~atm}\), what is the equilibrium pressure of \(\mathrm{WBr}_{4}(g)\) near the walls of the bulb? (b) Near the tungsten filament, where the temperature is about \(2800 \mathrm{~K}\), the reaction in part (a) has a \(K_{p}\) value of about \(5.0\). Is the reaction exothermic or endothermic? (c) When the \(\mathrm{WBr}_{4}(g)\) diffuses back toward the filament, it decomposes, depositing tungsten back onto the filament. Show quantitatively that the pressure of \(\mathrm{WBr}_{4}\) from part (a) will cause the reaction in part (a) to go in reverse direction at \(2800 \mathrm{~K}\). [The pressure of \(\mathrm{Br}(\mathrm{g})\) is still \(0.010 \mathrm{~atm}\). ] Thus, tungsten is continually recycled from the walls of the bulb back to the filament, allowing the bulb to last longer and burn brighter.

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