Huistaak Hoofdstuk 7 - Mastering Chemistry 1 Ba Revaki PDF

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Mastering Chemistry 1 Ba REVAKI...

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10-4-2020

HUISTAAK Hoofdstuk 7

HUISTAAK Hoofdstuk 7 Due: 11:59pm on Wednesday, November 27, 2019 You will receive no credit for items you complete after the assignment is due. Grading Policy

Item 1 The following table shows the caloric values of three types of food in kilocalories per gram of food: Food type

Carbohydrates

Fat

Protein

4 kcal

9 kcal

4 kcal

1g

1g

1g

Caloric value

Alexandra decides to climb Mt. Krumpett, which is 5000 m high. She determines that this will require a total of 2250 kcal of energy for the trip. For her food supply she decides to take nutrition bars. The label states that each bar contains 50 g of carbohydrates, 10 g of fat, and 40 g of protein.

Part A How many nutrition bars should Alexandra pack? Express the number of bars numerically.

Hint 1. Calculate the energy from carbohydrates How much energy comes from carbohydrates in one nutrition bar? Express your answer numerically in kilocalories. ANSWER: 200 kcal

Hint 2. Calculate the energy from fat How much energy comes from fat in one nutrition bar? Express your answer numerically in kilocalories. ANSWER: 90.0 kcal

Hint 3. Calculate the energy from protein How much energy comes from protein in one nutrition bar? Express your answer numerically in kilocalories. ANSWER: 160 kcal

Hint 4. Calculate the total energy in a nutrition bar What is the total amount of available energy in one nutrition bar? Express your answer numerically in kilocalories. ANSWER: 450 kcal

ANSWER: 5 bars

Correct

Item 2 The energy required to dissociate atoms of a compound is called the bond dissociation energy. This bond dissociation energy defines the strength of a covalent bond. The higher the bond dissociation energy, the more stable the bond between the atoms or ions. Chemical reactions that absorb heat, such as the dissociation of bonds, are called endothermic reactions, whereas chemical reactions that release heat, such as the formation of bonds, are called exothermic reactions. The difference between the heat energy absorbed in breaking bonds and the heat energy released in forming bonds is called the heat of reaction, or enthalpy change, and is represented by ΔHDeltaH. For an exothermic reaction, ΔHDeltaH is negative, and for an endothermic reaction, ΔHDeltaH is positive.

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The table lists the amount of energy associated with the dissociation of bonds between common elements. Bond dissociation energy (kJ / mol )

Bond

Bond dissociation energy (kJ / mol)

N − N

160.

C = C

614

N − H

391

C ≡ C

839

Bond

C − C

347

C = O

745

C − H

413

O = O

498

H − H

432

N = N

418

O − H

467

N ≡ N

946

C − O

358 * The C = O bond dissociation energy in CO2 specifically is 799 kJ / mol .

Part A Use the table of bond dissociation energy values given in the introduction to rank the following compounds based on the energy required to break the bond. Rank the compounds in increasing order of their bond dissociation energy. To rank items as equivalent, overlap them.

Hint 1. How to approach the problem You may follow these steps to rank the compounds: 1. Identify the single, double, and triple bonds in the given compounds. 2. Identify and compare the bond dissociation energy associated with each type of bond by referring the table in the introduction. 3. Now, rank the compounds in increasing order of their bond dissociation energies. Hint 2. Identify the trend in dissociation energies Rank the following nitrogen compounds from lowest to highest dissociation energy based on the table in the introduction. Rank the compounds in increasing order of their bond dissociation energy. To rank items as equivalent, overlap them. ANSWER:

Reset

HN = NH

H 2 N − NH 2

Help

\rmN ≡ N

ANSWER:

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HC ≡ CH

O =O

H−H

H 2 C = CH 2

H 3C − H

Help

H 2N − H

Correct Notice that the bond dissociation energies generally increase as the bond order increases. The carbon-carbon single bond takes 348 kJ / mol to break, whereas the carbon-carbon double bond takes 614 kJ / mol to break, and the carbon-carbon triple bond takes 839 kJ / mol . It takes more energy to break all three bonds of a triple bond than the one bond of a single bond.

Part B Natural gas is used in homes for central heating. The combustion of natural gas is represented by the equation CH 4 + 2O 2 → CO2 + 2H 2O Complete the table that identifies the bonds and the number of times each bond occurs for the given balanced chemical equation. Drag the appropriate labels to their respective targets.

Hint 1. How to approach the problem You may follow these steps to identify the number and types of bonds: 1. Determine the structure of the chemical compounds in the reactants and products. 2. Identify the types of bond in each compound based on the structures. 3. Determine the total number of each type of bond in each compound in the reactants and products. 4. Multiply the number of bonds in the compound with the coefficient to get the total number of bonds for the reaction. Hint 2. Identify the structures for the chemical compounds in the reactants and products Match the compounds involved in the given reaction to their structures showing the correct covalent bonds. Drag the appropriate labels to their respective targets. ANSWER:

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Help

Hint 3. Determine how coefficients impact the number of bonds The coefficient in a balanced chemical reaction indicates the number of molecules. You can multiply the coefficient by each characteristic of a molecule to determine how many times it occurs in the balanced chemical reaction. For example, for a term 3H2, you can multiply the coefficient three by the subscript two to determine that six atoms of hydrogen are represented by that term. Calculate the number of bonds represented by the term 2H 2O. Express your answer as a whole number. ANSWER: 4

ANSWER: Reset

H−O

C−C

O=O

C−H

C=O

O−O

C−O

4

1

3

Group 1

Group 2

Group 1

Group 2

Group 1

Group 2

Group 1

Group 2

Help

2

Correct For the reaction CH4 + 2O2 → CO2 + 2H2O, there are four C−H and two O 2 bonds associated with the reactants. There are two C=O and four O−H bonds associated with the products. This information can be used to calculate the heat of reaction for the combustion.

Part C https://session.masteringchemistry.com/myct/assignmentPrintView?assignmentID=8107979

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The heat of reaction for a chemical reaction can be calculated by finding the sum of the bond energies of the products and subtracting that from the sum of the bond energies of the reactants: Heat of reaction

= =

Sum of the energy for the bonds broken − Sum of the energy for the bonds formed Sum of reactant bond energies − Sum of product bond energies

When calculating the sum of the bond energies, each bond in the reaction must be accounted for. For example, CH 4 is a reagent with a coefficient of 1 in the reaction. There are four C−H bonds in methane and one methane molecule per reaction, for a total of four C−H bonds on the reactant side. All four bonds must be accounted for when finding the sum of the bond energies for the reactants. Calculate the heat of reaction using the average bond dissociation energies given in the introduction and your answer to Part B for the reaction CH 4 + 2O 2 → CO2 + 2H 2O Express your answer in kilojoules per mole to three significant figures.

Hint 1. How to approach the problem You may follow these steps to calculate the heat of reaction: 1. Calculate the bond dissociation energy for each reactant and product in the balanced chemical reaction by referring to the table given in the introduction. Use the table you developed in Part B to determine the total number of each type of bond in each term in the balanced chemical equation. 2. Add the bond dissociation energies of the reactants. For example, if there are four C−H bonds in CH4, then you need to multiply the bond dissociation energy for C−H by 4 to determine the energy contributed by CH4. Bond dissociation energy reactants = Sum of bond dissociation energy for CH4 bonds + Sum of bond dissociation energy 2O2 bonds 3. Add the bond dissociation energies of the products. Bond dissociation energy products = Sum of bond dissociation energy for CO2 bonds + Sum of bond dissociation energy for 2H2O bonds 4. Now, subtract the bond dissociation energy of the products from the reactants. The result is the heat of reaction for the given reaction: Heat of reaction, ΔHDeltaH = ΣSigma(bond dissociation energy) reactants - ΣSigma(bond dissociation energy) products where the symbol ΣSigma means "the sum of." Hint 2. Determine the bond dissociation energy for reactants Use the table of bond dissociation energies in the introduction to calculate the bond dissociation energy of the reactants. Express your answer in kilojoules per mole to four significant figures.

Hint 1. Determine the bond dissociation energy for methane Carbon forms four bonds with hydrogen in the CH 4 molecule. Use the table in the introduction to find the average bond dissociation energy for the C−H bond, and then use this to calculate the bond dissociation energy for all bonds in a CH4 molecule. Express your answer in kilojoules per mole to four significant figures. ANSWER: The bond dissociation energy of CH4 = 1652 kJ / mol

Hint 2. Determine the bond dissociation energy for the oxygen molecules There are two oxygen, O 2, molecules in the balanced chemical equation. Use the table in the introduction to find the average bond dissociation energy for a single O=O bond, and then use this to calculate the bond dissociation energy for all bonds associated with the term 2O 2. Express your answer in kilojoules per mole to three significant figures. ANSWER: The bond dissociation energy for the term 2O 2 = 996 kJ / mol

ANSWER: The bond dissociation energy for reactants = 2648 kJ / mol

Hint 3. Determine the bond dissociation energy for products Calculate the bond dissociation energy for products. Express your answer in kilojoules per mole to four significant figures.

Hint 1. Determine the bond dissociation energy for carbon dioxide Carbon forms two double bonds with oxygen in a CO2 molecule, as shown in Hint 2 of Part B (you can click Review Part). Calculate the bond dissociation energy for carbon dioxide, CO 2, using the data in the table in the introduction. Notice that there are additional values given below the table in the introduction.

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HUISTAAK Hoofdstuk 7 Express your answer in kilojoules per mole to four significant figures. ANSWER: The bond dissociation energy for CO2 = 1598 kJ / mol

Hint 2. Determine the bond dissociation energy for the water molecules There are two water, H 2O, molecules in the balanced chemical equation, each with two O−H bonds, as shown in Hint 2 of Part B (you can click Review Part). Calculate the bond dissociation energy associated with the term 2H2O. Express your answer in kilojoules per mole to four significant figures. ANSWER: The bond dissociation energy for the term 2H 2O = 1868 kJ / mol

ANSWER: The bond dissociation energy of products = 3466 kJ / mol

ANSWER: -818 kJ / mol

Correct 818 kJ are released for each mole of reactants as written. That is, when one mole of methane or two moles of oxygen burn, 818 kJ are released. When four moles of oxygen burn, 818 × 2 = 1632 kJ are released. As expected, the combustion produces energy.

Item 3 The heat of reaction, ΔHDelta H, is the amount of heat absorbed or released during a chemical reaction. It is calculated as the difference in energy of the product and the reactants.

Part A Label the energy diagram by matching each term to the appropriate letter from the graph. Drag each item to the appropriate bin.

Hint 1. How to interpret the graph The graph shows the potential energy of the system over the course of the reaction. The graph should be read left to right. In other words, A represents the potential energy before the reaction has started, and D represents the potential energy after the reaction has finished.

ANSWER:

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energy of reactants

activation energy

heat of reaction

Help

energy of products

Correct Notice in the diagram that the energy of the products is higher than the energy of the reactants. Therefore, we know that this is an endothermic reaction with a positive ΔHDelta H value.

Part B The energy diagram shown represents the chemical reaction between solid ammonium chloride and solid barium hydroxide octahydrate: 2NH4Cl(s) + Ba(OH)2 8H2O(s) → 2NH3(aq) + BaCl 2(aq) + 10H 2O(l) The ΔHDelta H for this reaction is 54.8 kJ . How much energy would be absorbed if 27.3 g of NH4Cl reacts? Express your answer with the appropriate units.

Hint 1. How to approach the problem First, convert the mass of NH4Cl to moles. Then, use the heat of reaction, ΔHDelta H, to calculate the amount of energy that was absorbed. The given ΔHDelta H value tells us that 54.8 kJ of heat is absorbed per 2 moles of NH4Cl (because of the coefficient of 2 in the chemical equation). This equality can be expressed as a conversion factor: 54.8 kJ 2 moles NH4Cl

We could then use that conversion factor to find the energy associated with any amount of NH4Cl . For example, the reaction of 1.00 mole of NH4Cl produces half as much energy as the reaction of 2 moles: 1.00 mole NH4Cl ×

54.8 kJ 2 moles NH4Cl

= 27.4 kJ

Follow this same procedure with the given amount of NH4Cl (just be sure to convert to moles first). Hint 2. Calculate the number of moles The molar mass of NH4Cl is 53.5 g / mole . Convert 27.3 g of NH4Cl to moles. Express your answer with the appropriate units. ANSWER: 0.510 mol

Correct Since 54.8 kJ of heat is absorbed per 2 moles of NH4Cl , you can now apply the conversion factor 54.8 kJ 2 moles NH4Cl

to convert from moles of NH4Cl to kilojoules.

ANSWER:

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energy absorbed = 14.0 kJ

All attempts used; correct answer displayed The reaction between Ba(OH)2 8H2O and ammonium salts absorbs so much energy from its surroundings that water coming in contact with the container will freeze.

Item 4 Learning Goal: To learn how temperature, concentration, and catalysts affect the rate of a reaction. The rate of a reaction is defined as the ratio of the change in concentration of a product to the change in time: rate of reaction =

changein concentration changein time

Three major factors will affect the rate of the reaction: temperature, concentration, and catalysts. In general, an increase in temperature, an increase in reactant concentration, or the presence of a catalyst will all increase the rate of the reaction. Ammonia, NH3, is used in numerous industrial processes, including the production of pharmaceuticals such as sulfonamide and antimalarials and vitamins such as the B vitamins. The equilibrium equation for the synthesis of ammonia (sometimes known as the Haber process) is N 2(g) + 3H 2(g)

2NH3(g)

Part A The Haber process is typically carried out at a temperature of approximately 773 K (500 C). What would happen to the rate of the forward reaction if the temperature were lowered to 373 K (100 C)?

Hint 1. Conditions for collisions The reactants are gases. Imagine the gas molecules bouncing around inside a container. Three conditions must be met for two molecules to react with one another: 1. The molecules must collide. 2. The molecules must align properly during the collision. 3. The collision must occur with enough energy. The minimum energy is called activation energy. Hint 2. How does temperature affect collisions? Chemical reactions occur when molecules collide. Determine how changes in temperature affect collisions. Drag each question into the bin with its correct answer.

Hint 1. Relating kinetic energy and temperature A change in temperature changes the kinetic energy and speed of the molecules.

ANSWER:

Reset

Help

Does a change in temperature affect how often the molecules collide? Does a change in temperature affect the orientation of molecules during a collision?

Does a change in temperature affect the energy with which molecules collide?

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ANSWER:

increase The reaction rate would

decrease

.

not change

Correct Most reactions double in rate for each 10 K (10 C) increase in temperature.

Part B What would happen to the rate of the forward reaction if the concentration of nitrogen were decreased?

Hint 1. Conditions for collisions The reactants are gases. Imagine the gas molecules bouncing around inside a container. Three conditions must be met for two molecules to react with one another: 1. The molecules must collide. 2. The molecules must align properly during the collision. 3. The collision must occur with enough energy. The minimum energy is called activation energy. Hint 2. How does concentration affect collisions? For ammonia to be produced, nitrogen must collide with hydrogen. Determine how changes in concentration affect collisions. Drag each question into the bin with its correct answer.

Hint 1. Probability of collision The more molecules there are in a given space, the greater the chance that two of them will collide. If there are fewer molecules in a given space, there is less of a chance that two of them will collide.

ANSWER:

Reset

Does a change in concentration affect the orientation of molecules during a collision?

Help

Does a change in concentration affect how often the molecules collide?

Does a change in concentration affect the energy with which m...