Chapter 6 Answers and Explanations

Chapter 6 Answers and Explanations

• All of the reactants and products are shown in the answer.
• There are species that appear on both sides.
• That leaves 2A + C - E 2.

• Species B is a catalyst, as it is present before and after the reaction, but it doesn't show up in the equation.
• The order of the reaction is not changed by catalysts, they simply lower the activation energy so the reaction can proceed more quickly.
• The reaction would take place without a catalyst, but it would take a long time.

• Rate laws only have reactants in them.
• In Step II, you can replace C with A + B, as these are the same as in Step I.

• As Step II is the slow step, the coefficients become exponents in the overall rate law.

• The speed of the molecule increases when the temperature is increased.
• A successful collision is more likely to happen because of this.
• It is more likely that the collision will exceed the energy barrier because there will be more energy within it.

• The half-life of the reactant would need to increase if none of the options were used.

• The coefficients on the reactants in the slowest elementary step match the coefficients on the reactants in the overall rate law.
• B is not present at the start of the reaction and therefore cannot be included in the rate law.
• When the rate law is determined, the 2A can be replaced for B in the slow step if B is in equilibrium with 2A in the first step.

• For every NO molecule that forms, two other NO molecule must disappear, so NO is appearing at the same rate.

• The coefficients of the reactants can be used to determine the rate law for the slowest elementary step.
• The overall order can be obtained by adding the rates in the rate law: 1 + 1 and 2.

• The rate doubles when B is doubled and A is held constant.
• The reaction is first order with respect to B.

• When A is doubled and B is held constant, the rate doesn't change.

• That means that the reaction is zero order with respect to A and that A will not be included in the rate law.

• Light absorbance is read by a spectrophotometer.
• A red solution appears to be red.
• The amount of light reflected by the solution does not change as the solution gets smaller.
• The solution is red because the wavelength of red light matches the distance between the energy levels.

• The rate doubles when B is doubled and A is held constant.
• The reaction is first order with respect to B.

• When A and B are doubled, the rate increases by a factor of 4.
• The doubling of A must also change the rate by a factor of 2 because the rate is in fact multiplied by 4.

• The key to this question is to know that reactant A is disappearing with a half-life.
• The reaction is first order with respect to A.

• A chart can be made.
• Always start at a certain time.

• It takes two half-lives for the amount to decrease.
• One half-life must be 22 minutes if two half-lives take 44 minutes.

• When you compare the results of the first and second experiments, you can see that the reaction is first order with respect to B.

• You're left with a balanced equation if D's cancel.

• The slow, rate determining step is the first part of the mechanism because it is the same as the experimentally determined rate law.

• The results of experiments 1 and 3 show that when the rate doubles, the reaction is first order.

• 2 moles of NO are consumed for every mole of Br2.

• Replacing the N2O2 with 2NO is the first step in the proposed mechanism.

• The rate law for the elementary step is the same as the overall rate law.

• This type of decay is typical of a first order reaction.

• The rate of appearance of P4 will decrease.

• The reaction will go faster at a higher temperature.
• It will take less time for the phosphine to decay.

• The relationship between the rate constant and temperature is proportional.
• The rate will be constant as the temperature increases.

• The rate constant is unaffected by the concentration of the reactants.

• The rate is independent of the concentration of B if the reaction is zero order.

• The rate constant is unaffected by the concentration of the reactants.

• The rate constant increases when the temperature increases because more gas molecule collide with enough energy to overcome the activation energy for the reaction.

• The rate constant is unaffected by the concentration of the reactants.

• Adding a catalyst makes it easier for the reaction to occur.

• The distribution will shift to the right at a higher temperature because more of the molecule will be at higher energies.

• The ln[reactant] changes in a linear fashion over time, as shown in the following equation.

• The Raschig process can be used to produce hydrzine.

• To determine the net equation, all three equations must be added together, and species that appear on both sides of the arrow can be eliminated.

• 2Cl, N2H5 and OH- are intermediates in the process.

• Justify your answer.

• The rate law will match the slowest step.
• The rate law of an elementary step can be determined by the reactants present, and in this case, the rate law for Step 1 matches the overall rate law.

• The fastest step is Step 1.

• The calculated rate of disappearance would decrease if the student waited 30 seconds.

• A straight line in a graph of ln [CV+] vs. time can be created by a reaction that is first order.

• The rate of reaction doubled, meaning that there is a direct relationship between the rate and the reaction.

• The laws of energy explain and predict the direction of changes in matter.

• Many people don't know that heat and temperature are not the same.
• The concepts are related, but they represent different things.
• The amount of energy in the universe is constant.

• As the faster moving molecule collides with the slower one, they transfer some of their energy, changing the speed of both of them.
• When studying the energy flow that takes place with many physical and chemical processes, the terms exothermic and endothermic can be defined in a different way.
• Energy is transferred from the reaction to its surroundings in an exothermic process.
• The process of dissolving salt in water emits energy, which causes the water temperature to increase.
• The water absorbed it.

• The opposite is true for an endothermic process.
• When an ice cube is in your hand, the energy leaves your hand and goes into the ice cube.

• This is an endothermic process.
• Both physical and chemical changes can be classified as endothermic.

• They all depend on the change between the initial and final states of the system.

• The values of the quantities are usually given for standard state conditions when they are given on the test.

• All gases are under pressure.

• The room temperature is almost indistinguishable from the standard state values.
• State values can be calculated for other temperatures.

• When one mole of a compound is formed from its component pure elements under standard state conditions, it is known as heat of formation.
• The temperature at which the thalpy of formation is calculated is 25degC.

• An enthalpy of formation equation is shown.

• When that product has an odd number of atoms from an element that is diatomic in nature, it's a good idea to use halves to balance the equation.

• This is true for elements that are in their pure state.

• The process is cold.

• The process is endothermic.

• The units for reaction enthalpy are kJ/molrxn.

• When 2 moles of CH3OH react with 3 moles of oxygen, 1354 kJ of energy is released.

• The amount of energy released when one mole of a hydrocarbon combusts is known as the enthalpy of combustion.
• When discussing the enthalpy of combustion, we often see halves used to balance the diatomic oxygen molecule that is always part of a combustion reaction.
• The enthalpy change is half of the calculated one, as we are burning half as much methanol.
• Reactions are rarely in exact quantities.
• To determine the energy change, you have to combine the two concepts.

• The prompt tells us that CH3OH is the limiting reactant.

• We would have to determine which reactant was limiting.
• The limiting reactant limits the amount of products formed and the amount of heat change that occurs during the reaction.

• 106 kJ of energy is released.
• When doing thermodynamics problems, mole ratios should be taken into account.
• If you are given a specific amount of reactants and asked about the energy change for a reaction, you will have to use a method called stoichiometry to get the correct answer.

• The energy needed to break a bond is called bond energy.
• Bond energy is always a positive number because the breaking of a bond is an endothermic process.

• The bond energy is equal to the bond energy.

• The bonds that are broken will be the reactant bonds and the bonds that are formed will be the product bonds.

• The number of bonds broken and formed is affected by the number of bonds within a molecule as well as how many of those bonds are balanced.
• Each water molecule has two O-H bonds, and there are two water molecule present in the equation below.

• There are three rules for manipulating equations in enthalpy calculations.

• The sign on the enthalpy value should be flipped if you flip the equation.

• If you divide an equation by the same number, you should also divide it by the same number.

• The enthalpy values of component equations can be added to a new equation if several equations are summed up.

• We want to make sure the products and reactants are on the correct side of the equation.
• We'll leave the other two reactions alone because all other species seem to be on the same side.

• Fortunately, the two O2 on the products side add up to 5, and both the N2 and H2 cancel out completely, giving us the final equation that we wanted.
• The final enthalpy will be 361.2 + 183.6 - 1451.

• A certain amount of heat is released or absorbed when an ionic substance is dissolved in water.
• The bond between the cation and anion is breaking, which requires energy, but energy is released when those ion form new attractions to the water molecule.
• The process can be broken down into three steps.
• For this example, we will use NaCl dissolving in water.

• The bonds between the two ion groups must be broken.
• The amount of energy needed to break this bond is the same as the lattice energy.

• The water must be spread out to make room for the Na+.

• The last step involves the free-floating ion being attracted to the water molecule.
• While bonds are not being formed, energy is still being released.

• The magnitude of the energy change in step 3 is greater than the magnitude of the energy change in step 2.
• As with lattice energy, hydration energy is a Coulombic energy and increases as the ion increases in charge or decreases in size.

• The enthalpy of solution for that compound can be determined if you add the energy values for all three steps together.
• The enthalpy of solution is negative if the hydration energy exceeds the lattice energy.
• The enthalpy of solution is positive if lattice energy exceeds hydration energy.

• Changes in temperature and pressure are what cause phase changes.

• Phase changes do not involve breaking bonds or the creation of new substances.

• Some particles in a liquid or solid can break away from the surface and become gaseous.
• When the gas phase of a substance is in equilibrium with the liquid phase, the pressure of the gas will be equal to the vapor pressure of the substance.
• Vapor pressure of a liquid will increase as temperature increases.
• The liquid will boil when the vapor pressure of the liquid increases to the point where it is equal to the atmospheric pressure.

• The forces holding the solid together need this energy to be overcome.

• The heat of fusion comes from the substance when it freezes.
• The intermolecular forces within a solid are more stable than the forces within a liquid, so energy is released in the freezing process.

• The liquid is being held together by forces.
• The heat of vaporization is the heat given off by the substance.
• When a gas condenses, it becomes a liquid, which is more stable, and energy is released.

• When heat is added to a substance, it can increase or decrease in temperature, but not at the same time.
• The temperature of the substance remains constant when it is changing phases.

• Below is the phase diagram for water.

• The solid-liquid equilibrium line slopes upward in the phase diagram for substances other than water.
• When pressure is increased, a normal substance will change from liquid to solid, but water will change from solid to liquid.

• Water's hydrogen bonds form a lattice structure when it is cold.
• The solid phase is less dense than the liquid phase because of this.

• That's the reason ice floats on water.

• The amount of heat required to raise the temperature of a gram of substance by one degree Celsius is called the specific heat.

• The easiest way to think about this is to consider the temperature changes you experience when wearing a black shirt as opposed to a white shirt on a hot summer day.
• You are absorbing the same amount of heat even if you are wearing a different shirt.

• The enthalpy can be determined by determining the amount of heat transfer in a reaction.

• The reaction occurs when NaOH are mixed together in a cup.
• Over the course of the reaction, the temperature rises from 23.00degC to 31.60degC.
• The enthalpy of the reaction is determined by the density of the solutions and the specific heat of the mixture.

• To solve this, we need to know how much heat was released during the reaction.
• The mass of the final solution can be determined by taking the total volume of the solution and dividing it by the density.
• The temperature is 8.60degC.
• We need to know how many moles of product are formed in this reaction.
• We can see that there will be less of the HCl, which has a lower molarity and volume.
• We can use the HCl to determine how many moles of product will form because everything here is in a1:1 ratio.

• The heat gain from earlier was due to the water.
• The heat is lost due to the reaction itself.
• To calculate the enthalpy of reaction, we have to flip that sign to show heat is lost, and then divide that value by the number of moles.

• The amount of heat given per mole of product is called enthalpy.
• In situations where it is not easy to determine which reactant is limiting, limiting reagent calculations can be done.

• You must add the mass of the solid to the mass of the water in order to do your calculations.
• The final mass of the solution is 208.0 g, which is the density of water.

• A cooling curve shows what happens to the temperature of a substance when heat is added.
• The temperature of the substance will increase if it is in a single phase.
• calorimetry can be used to calculate the amount of the temperature increase.
• The amount of heat required to cause a substance to change phases can be calculated using the heat of fusion or the heat of vaporization.

• It is important to pay close attention to what your units are when doing calculations because there are a lot of different units that can be used.

• A 1.53 g piece of ice is in the freezer at a temperature of -15.1degC.

• The ice is removed from the freezer after it reaches a certain temperature.

• There are two parts to the problem.
• The temperature change of the ice is the first part.

• The ice is melting.
• The number of moles of ice must be determined first.

• The two values can be added together.

• All substances that we encounter will have some positive value for the zero entropy that is defined as a solid crystal at 0 K.

• There are a number of simple rules regarding entropies.

• Liquids have higher values.

• Gases have higher values than liquids.

• The particles in the solution have higher values.

• Two moles of a substance have a higher value than one mole.

• A process that occurs without outside energy input is said to be more favorable than a process that does not.
• This text will use the updated terms, but it would be good for you to be familiar with both sets of terms.

• Nature likes to move toward two different states--low energy and high disorder--so thermodynamically favored processes must result in decreasing enthalpy or increasing entropy.

• You should make sure your units match up here.

• The values of enthalpy and entropy are shown in the chart.

• At low temperature, enthalpy is more dominant than at high temperature.

• If the potential is positive, a redox reaction will be favored.
• A negative value for free-energy change can be found in thermodynamics.
• The equation below shows the relationship between reaction potential and free energy for a redox reaction.

• There are a few important things we can see from this equation.

• Let's look at an example.

• The units on the free energy are in J/mol and not kJ/mol, so the answer comes out in joules instead of kilojoules.

• The following information can be used to answer questions.

• The reactant molecule would collide more often, which would make it more positive.

• The gases will be at a higher pressure, which would make it more negative.

• It's favored at low temperatures.

• It is favored at high temperatures.

• Increasing the temperature of the reaction can increase the product yield.

• The speed of the molecule will increase if the temperature is increased.

• The reactants are less massive than the products, and an increase in temperature will cause their energy to increase more than that of the products.

• The increase in temperature makes it possible for a higher percentage of collisions to occur with the proper orientation.

• The temperature goes up by 2.2degC when 1.50 g of NaNO3 is dissolved into water.
• The final solution has a density of 1.02 g/mL.
• The volume of the solution should not change.

• A solid substance is being heated.
• It first becomes a liquid and then becomes a gas.

• Solution A has a volume of 100 mL.
• The solution B has a volume of 1000 mL.

• The heat capacity of solution A is greater than that of solution B.

• The heat would transfer from B to A if the solutions were mixed.

• The reaction is favored at 1.0 atm.

• The following diagram can be used to answer questions.

• The distance between points 2 and 4 would be reduced.

• The slope of the line would increase.

• The reaction is transferred to the surroundings.

• The products are transferred from the reactants.

• The products are transferred to the reactants.

• The following information can be used to answer questions.

• The temperature of the water increases when calcium chloride is dissolved.

• The hydration energy between the water molecule and the solute ion is greater than the lattice energy.

• The hydration energy must be greater than the strength of the intermolecular forces.

• The hydration energy needs to be greater than the strength of the intermolecular forces.

• The charges of fluoride and chloride are the same.

• The hydration energy is dependent on the amount of water present.

• The molar mass of CaF2 is smaller than that of CaCl2.

• A large increase in temperature is shown in the diagram below.

• It is an exothermic reaction.

• It is an endothermic reaction.

• It is an endothermic reaction.

• A metabolism reaction that takes place in the body releases energy.

• The diagram shows how heat can change the temperature of a covalent substance.

• Justify your answer.

• Justify your answer.

• The table has several bond enthalpies listed.

• Justify your answer.

• A student is trying to determine the heat of aluminum.
• A student drops a piece of aluminum with a mass of 5.86 g into a calorimeter with 25.0 liters of water.

• If the density of the water is exactly 1.00 g/mL, then calculate the heat gained by the water.

• Make sure that any identified error can be tied to the student's results.