The diagram below represents an interpretation of Hess's law for the following reaction

How does the enthalpy of the products of a reaction system compare with the enthalpy of the reactants when the reaction is a. endothermic? b. exothermic?

a. Distinguish between enthalpies of reaction, formation, and combustion. b. On what basis are enthalpies of formation 13 and combustion defined?

Write the equation that can be used to calculate the enthalpy of reaction from enthalpies of formation.

What factors affect the value of LxH in a reaction system?

State Hess's law. How is it used?

Describe a combustion calorimeter. What information can it give?

How much energy is needed to raise the temperature of a 55 g sample of aluminum from 22.4C 15. to 94.6C? Refer to Table 1 for the specific heat of aluminum. (Hint: See Sample Problem A.)

If 3.5 kJ of energy are added to a 28.2 g sample of iron at 20C, what is the final temperature of the iron in kelvins? Refer to Table 1 for the specific heat of iron.

You need 70.2 J to raise the temperature of 34.0 g of ammonia, NH3(g), from 23.0C to 24.0C. Calculate the specific heat of ammonia.

Calculate c, for indium metal, given that 1.0 mol In absorbs 53 J while increasing in temperature from 297.5 K to 299.5 K.

For each equation listed below, determine the till and type of reaction (endothermic or exothermic). 17. a. C(s) + 02(g) -p CO2(9) + 393.51 kJ b. CH4(9) + 202(g) -+ CO2(9) + 2H200) + 890.31 kJ c. CaCO3(s) + 176 kJ -* CaO(s) + CO2(g) d. H20(g) -p H20(1) + 44.02 kJ

Rewrite each equation below with the Ml value included with either the reactants or the products, and identify the reaction as endothermic or exothermic. a. H2(9) + 02(g) -p H200); AJ10 =28583 kJ b. 2Mg(s) + 02(g) -+ 2MgO(s); C- 12(5) - 12(9); MI = +62.4 kJ d. 3C0(g) + Fe203(s) -* Ye(s) + 3CO2(g); AHO = 24.7 U

Use Appendix Table A-14 to write the reaction illustrating the formation of each of the following compounds from its elements. Write the tiH as part of each equation, and indicate the AH for the reverse reaction. a. CaC12(s) b. C21-12(g) (ethyne, or acetylene) C- SO2(g)

The reaction 217e203(s) + 3C(s) -+ 417e(s) + 3CO2(9) is involved in the smelting of iron. Use M-11 values given in Appendix Table A-14 to calculate the enthalpy change during the production of 1 mol of iron.

Use enthalpy-of-formation data given in Appendix Table A-14 to calculate the enthalpy of reaction for each of the following. Solve each by combining the known thermochemical equations. Verify each result by using the general equation for finding enthalpies of reaction from enthalpies of formation. (Hint: See Sample Problem B.) a. CaCO3(s) -* CaO(s) + CO2(9) b. Ca(OH)2(s) -+ CaO(s) + H20(g) c. Fe203(s) + 3CO(g) -) 213e(s) + 3CO2(9)

For glucose, C6H1206(s), AHf= 1263 kJ/mol. Calculate the enthalpy change when 1 mol of C6H1206(s) combusts to form CO2(g) and H2O(1).

Calculate the standard enthalpies of reaction for combustion reactions in which ethane, C2H6, and benzene, C6H6, are the respective reactants and CO2(g) and H20(l) are the products in each. Solve each by combining the known thermochemical equations using the tiHf values in Appendix Table A-14. Verify the result by using the general equation for finding enthalpies of reaction from enthalpies of formation. a. C2H6(9) + 02(g) -f b. C6H6(l) + 02(g) -p

The enthalpy of formation of ethanol, C2H50H, is -277.0 kJ/mol at 298.15 K. Calculate the enthalpy of combustion of one mole of ethanol, assuming that the products are CO2(g) and H20(1). (Hint: See Sample Problem C.)

Would entropy increase or decrease for changes in state in which the reactant is a gas or liquid and the product is a solid? What sign would the entropy change have?

How does an increase in temperature affect the entropy of a system?

What combination of AR and AS values always produces a negative free-energy change?

Explain the relationship between temperature and the tendency for reactions to occur spontaneously.

A reaction has AH = -356 kJ and AS = -36 J/K. Calculate AG at 25C to confirm that the reaction is spontaneous.

A reaction has AN = 98 kJ and AS = 292 J/K. Investigate the spontaneity of the reaction at room temperature. Would increasing the temperature have any effect on the spontaneity of the reaction?

A reaction has All = -76 kJ and AS = -117 J/K. Calculate AG for the reaction at 298.15 K. Is the reaction spontaneous?

The gas-phase reaction of H2with CO2to produce H20 and CO has AN = 11 kJ and AS =41 J/K. Is the reaction spontaneous at 298.15 K? What is AG?

Based on the following values, compute AG values for each reaction and predict whether the reaction will occur spontaneously. (Hint: See Sample Problem D.) a. AH=-i-125 kJ, T=293K, AS = 0.0350 kJIK b. AH = -85.2 kJ, T = 127C, AS=0.125kJ/K c. AH=-275kJ,T=773K, AS = 0.450 k.JIK

The AS for the reaction shown, at 298.15 K, is 0.003 00 kJ/(mol.'K). Calculate the i.G for this reaction, and determine whether it will occur spontaneously at 298.15 K. C(s) + 02(g) - CO2(9) + 393.51 kJ

When graphite reacts with hydrogen at 300 K, AN is -74.8 U and AS is -0.0809 kJ/K. Will this reaction occur spontaneously?

How might you change reaction conditions to induce an endothermic reaction that does not occur naturally?

The diagram below represents an interpretation of Hess's law for the following reaction. Sn(s) + 202(g) -) SnCl4(1) Use the diagram to determine AN for each step and the net reaction. Sn(s) + C12(g) -+ SnC12(s) AN =? SnC12(1) + C12(g) -p SnCl4(s) AN =? Sn(s) + 2C12(g) -* SnC14(l) AN =? 0 Sn(s), C12(9) -100 - -325.1 kJ -200 - 7 -300 - -400 - SnCl2(s) 186.2 kJ -500 - SnCI4(I)

The standard enthalpy of formation for sulfur dioxide gas is -296.8 kJ/mol. Calculate the amount of energy given off in U when 30.0 g Of S02(9) is formed from its elements.

The thermite reaction used in some welding applications has the following enthalpy and entropy changes at 298.15 K. Assuming AS and All are constant, calculate AG at 448 K. Fe203+ 2A1(s) 217e(s) + A1203(s) AHO = 851.5 kJ AS = 38.5 J/K

Rewrite each equation below with the All value included in either the reactants or products, and identify the reaction as endothermic or exothermic. a. 2S02(9) + 02(g) * 2S03(9); AH= 197.8 kJ b. 2NO2(9) * 2N0(g) + 02(g); AH=+114.2 kJ c. C2H4(9) + 302(g) * 2CO2(9) + 2H20(l); AH=-1411.0 kJ

Calculate the change in enthalpy for the following reaction. 4FeO(s) + 02(g) * 2Fe2O3(s) Use the enthalpy-of-formation data listed in Appendix Table A-14.

The reaction to synthesize methanol (CH30H) industrially is CO(g) + 2112(9) CH30H(g). The A.Hacaon = 90.7 kJ and the AS reaction = 220.8 J/K. At what temperatures is the reaction nonspontaneous?

What is the main characteristic of a calorimeter in a bomb calorimeter experiment, and why is this characteristic essential?

Relating Ideas Given the entropy change for the first two reactions below, calculate the entropy change for the third reaction below. S8(s) + 802(5) 4 8S02(9) AS = 89 J/K 2S02(s) + 02(5) * 2S03(9) AS = 188 J/K S8(s) + 1202(5) * 8S03(9) AS =?

Interpreting Concepts Look at the two pictures below. Which picture appears to have more order? Why? Are there any similarities between the amount of order the marbles have and the entropy of particles? (a) (b)

Inferring Conclusions A reaction is endothermic and has a AH =8 kJ. This reaction occurs spontaneously at 25C. What must be true about the entropy change?

Inferring Conclusions If both AH and AS are negative, how does temperature affect spontaneity?

Inferring Relationships If the reaction X * Y is spontaneous, what can be said about the reaction Y * X?

Interpreting Concepts Absolute enthalpy cannot be determined; only change in energy can be measured. However, absolute entropy can be determined. Explain why an absolute entropy can be determined.

Obtain information on alternative units of measure used to express values of energy as heat and other forms of energy. Also, find out how the quantities relate to SI units. Include information specifically on English units, such as the British thermal unit (BTU), and on typical BTU ratings of household appliances. Calculate how these ratings would be expressed in joules instead.

Performance Design a simple calorimeter investigation to determine the molar enthalpy of fusion of water. Use the following materials: a large plastic-foam cup with cover, a thermometer, a balance, water at room temperature, and an ice cube. Allow your teacher to review your design. Then carry out the investigation, and write a laboratory report including your calculations and a comparison of your quantitative results with known values. Try to account for any disagreements between the experimental and actual values.

Performance Design an experiment to measure the molar heat capacities of zinc and copper. If your teacher approves the design, obtain the materials needed and conduct the experiment. When you are finished, compare your experimental values with those from a chemical handbook or other reference source.

Performance Develop a procedure to measure the EH of the reaction shown below. If your teacher approves your procedure, test your procedure by measuring the All value of the reaction. Determine the accuracy of your method by comparing your All with the accepted All value. CH3COONa(s) + Na(aq) + CH3COO(aq)