CP Chemistry Unit 10 Thermodynamics-Test Plan

Essential Vocabulary: Work Heat System Surroundings Internal energy Specific heat Calorimeter Joule Celsius Enthalpy of reaction (ΔHrxn) Heat of formation (ΔHf) Hess’ Law

Essential Outcomes: Know the sign convention for heat and work entering or exiting the system. Be able to calculate the internal energy of a system (ΔE = q + w) Be able to relate the change in temperature of a substance to the heat

absorbed or released (q = mCΔT) Be able to calculate the specific heat capacity of a metal using calorimetry. Be able to measure the ΔHrxn using calorimetry Be able to convert joules to kilojoules Be able to calculate the enthalpy of reaction for different gram amounts of a

reactant or product. Be able to predict the change in enthalpy when a reaction is reversed or the

stoichiometry is changed. Be able to apply Hess’ Law. Be able draw a reaction that represents the heat of formation of a compound. Be able to use heats of formation to determine the ΔHrxn of a reaction.

(∑ΔHproducts- ∑ΔHreactants) Be able to identify the thermodynamics of a reaction from a reaction

coordinate (energy diagram) For common qualitative experiences (such as the melting of ice), be able to

identify the situation as exothermic or endothermic and be explain why.

Energy Unit ConversionsPractice Problems

Answer in the space provided. Show your work for full credit!

Remember: 1 cal = 4.184 J

Perform the following conversions:1. 340. cal to joules

2. 75.6 joules to calories

3. 7200. kcal to cal

4. 12.9 kJ to J

5. 12755 J to kJ

6. Europeans food labels are often listed in kJ. How many calories were in this snack?

Heat, Work, and Internal Energy Practice

Word Bank

Work-

Heat -

System -

Surroundings -

Internal energy -

Specific heat -

Calorimeter -

Joule -

Enthalpy of reaction (ΔHrxn)

Heat of formation (ΔHfus)

Heat of dissolution (ΔHd)

Heat of vaportization (ΔHv)

Heat of formation (ΔHf)

Heat of combustion(ΔHcomb)

Hess’ Law

Energy of activation

Endothermic and Exothermic Reactions

Answer the following questions in the space provided. Show your work on calculations!1. Identify the following as either endothermic or exothermic:

a. ice melting

b. a firecracker going off

c. natural gas is burned in a furnace

d. when solid KBr is dissolved in water, the solution gets colder.

e. frost forming on the windows of a car overnight

f. When concentrated sulfuric acid is added to water, the solution gets very hot

2. The equation for the fermentation of glucose to alcohol and carbon dioxide isC6H12O6 2C2H5OH + 2CO2

The enthalpy change for the reaction is -67 kJ.a. Is this reaction endothermic or exothermic?

b How would the reaction feel to the touch?

b. Write the equation again below and include the energy term in the equation.

3. For the reaction

S + O2 SO2 ∆H = -296 kJ/mol

a. Is this reaction endo- or exothermic?

b. Rewrite the chemical equation with the energy term in the equation.

c. Draw a reaction coordinate diagram showing if the relative energy of the reactants and products. . Label the ∆H on the diagram.

4. Given the following reaction:

Fe3O4 + CO + 18 kJ 3FeO + CO2

a. Is this reaction endo- or exothermic?

b. How would the reaction feel to the touch?

c. What is the sign of the energy term when written in this form: ∆H =

d. Draw a reaction coordinate diagram showing the relative energy of the reactants and products. Label the ∆H on the diagram

5. For the following reaction

NO + O3 NO2 + O2 + 199 kJ

a. Is this reaction endo- or exothermic?

b. Write the energy term: ∆H =

c. How many moles of NO are reacted in the balanced equation?

d. Would you expect to produce more or less heat when 12 moles of NO are reacted?

e. How much heat would result from the 12 moles?

Enthalpy of Reaction (H) Practice

For each problem below, write the equation and show your work. Always use units.

1. The decomposition of limestone, CaCO3(s), into lime, CaO(s), and CO2(g) at constant pressure requires the addition of 178.1 kJ of heat per mole of CaCO3.

a. Write a balanced thermochemical equation for the reaction showing energy as a reactant or product.

b. Draw an enthalpy diagram for the reaction.

2. Consider the following reaction:CH3OH (g) --> CO (g) + 2 H2 (g) H = +90.7 kJ

a. Is the reaction exothermic or endothermic?

b. Calculate the amount of heat transferred when 45.0 g of CH3OH (g) are decomposed by this reaction at constant pressure.

c. If the enthalpy change is 16.5 kJ, how many grams of hydrogen gas are produced?

d. How many kilojoules of heat are released when 10.0 g of CO (g) reacts completely with H2 (g) to form CH3OH (g) at constant pressure?

3. At one time, a common means of forming small quantities of oxygen gas in the laboratory was to heat KClO3:

2KClO3 (s) --> 2 KCl (s) + 3 O2 (g) H = -89.4 kJ

For this reaction, calculate H for the formation of a. 1.24 mol of O2

b. 4.89 g of KCl

c. 1.76 g of KClO3 from KCl and O2

4. Consider the decomposition of liquid benzene, C6H6 (l), to gaseous acetylene, C2H2 (g):

1/3 C6H6 (l) --> C2H2 (g) H = +210 kJ

a. What is the enthalpy change for the reverse reaction?

b. What is H for the decomposition of 1 mol of benzene to acetylene?

c. Which is more likely to be thermochemically favored, the forward reaction or the reverse reaction?

d. If C6H6 (g), were consumed instead of C6H6 (l), would you expect the magnitude of H to increase, decrease, or stay the same? Explain.

Hess’ Law Practice

1. Calculate the heat of reaction for:PbCl2 (s) + Cl2 (g) PbCl4 (l) ∆ H = ?

by combining: Pb (s) + Cl2 (g) PbCl2 (s) ∆ H = - 359.4 kJPb (s) + 2 Cl2 (g) PbCl4 (l) ∆ H = - 329.3 kJ

2. From the following heats of reaction:2 SO2(g) + O2(g) 2 SO3(g) H = – 196 kJ2 S(s) + 3 O2(g) 2 SO3(g) H = – 790 kJ

Calculate the heat of reaction for:S(s) + O2(g) SO2(g) H = ? kJ

3. The standard heats of formation of HCl (g) and HBr (g) are -92.0 kJ/mol and -36.4 kJ/mol respectively. Using this information, calculate ΔH for the following reaction:

Cl2 (g) + 2 HBr (g) → 2 HCl (g) + Br2 (g)

 

4. Given the following equations:4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(l)   ΔH° = -1170 kJ4 NH3(g) + 3 O2(g) → 2 N2(g) + 6 H2O(l)    ΔH° = -1530 kJ

Using these two equations, determine the heat of formation, ΔHf° , for nitrogen monoxide, NO.

5. From the following heats of reaction:2 H2 (g) + O2 (g) 2 H2O (g) H = - 483.6 kJ3 O2 (g) 2 O3 (g) H = +284.6 kJ

Calculate the heat of the reaction for:3 H2 (g) + O3 (g) 3 H2O (g)

6. Given the following data:N2 (g) + O2 (g) 2 NO (g) H = + 180.7 kJ2 NO (g) + O2 (g) 2 NO2 (g) H = - 113.1 kJ2 N2O (g) 2 N2 (g) + O2 (g) H = - 162.3 kJ

Use Hess’s law to calculate Hrxn for the following reaction. N2O (g) + NO2 (g) 3 NO (g)

Heat of Formation Practice

1. Calculate Ho (in kJ) for these reactions. In each case, state whether the reaction is exothermic or endothermic, rewrite the equation as a thermochemical equation to include the heat term.

For example:  2 NO(g) + O2(g) ---> 2 NO2(g)

Hf = [2(33.2kJ) – ((2(90.3kJ))+(0kJ)) = -114.2 kJ

The reaction is EXOTHERMIC, and the thermochemical reaction should read:

2 NO(g) + O2(g) ---> 2 NO2(g) + 114.2 kJ

a) NaOH(s) + HCl(g) ----> NaCl(s) + H2O(g) 

b) SO2(g) + ½ O2(g) ---> SO3(g)

c) CaO(s) + H2O(l) ---> Ca(OH)2(s)

d) N2(g) + 3 H2(g) ---> 2 NH3(g)

e) C6H6(l) + 1½ O2(g) ---> 6 C(s) + 3 H2O(l) 

f) NH3(g) + HCl(g) ---> NH4Cl(s) g) Chemistry 30

2. Write heats of formation reactions for each of the following compounds in two ways, one as a reaction with the appropriate Hf value, and secondly, as a thermochemical reaction. You will need to refer to a Table of Thermochemical Data.

CuCl2 (g), N2H4 (l)  

 

3. The standard heat of formation, ΔHof, for sulfur dioxide (SO2) is -297 kJ/mol. How many kJ of energy are given off when 25.0 g of SO2 (g) is produced from its elements?

 

 

4. The heat of reaction for the combustion of 1 mol of ethyl alcohol is -9.50 × 102 kJ:

C2H5OH (l) + 3 O2 (g) → 2 CO2 (g) + 3 H2O (l) + 9.5 × 102 kJ

How much heat is produced when 11.5 g of alcohol is burned? 

5. ΔH for the complete combustion of 1 mol of propane is -2.22 × 103 kJ:

C3H8 (g) + 5 O2 (g) → 3 CO2 (g) + 4 H2O (l)

Calculate the heat of reaction for the combustion of 33.0 g of propane.

Calorimetry Practice q=m c ∆T

1. A 25.0 g sample of an alloy was heated to 100.0 oC and dropped into a beaker containing 90 grams of water at 25.32 oC. The temperature of the water rose to a final value of 27.18 oC. Neglecting heat losses to the room and the heat capacity of the beaker itself, what is the specific heat of the alloy?

2. The specific of solid iron is 0.477 J/goC. If 230 g of Fe at 95oC were placed in 1 L of water at 15oC, what would Tf be?

3. 101 g of an unknown metal at 50oC is placed in 40 g of water at 25.0oC. The temperature of the system at equilibrium is 29.7oC. What is the unknown metal? Your choices, and their Specific Heat values (in J/goC) are:

a. Ba (0.284)b. Cr (0.464)c. Cu (0.385)d. Au (0.130)e. Sn (0.213)f. Rb (0.360)g. Ti (0.594)

Heat of Reaction Lab: Hess’s Law

In this experiment, you will determine and compare the enthalpy changes in three thermodynamic reactions. Start by writing balanced chemical equations for each of the reactions.

Reaction 1: Solid sodium hydroxide dissolves in water to form an aqueous solution of ions.

Reaction 2: An aqueous solution of sodium hydroxide reacts with an aqueous solution of hydrogen chloride to form water and an aqueous solution of sodium chloride.

Reaction 3: Solid ammonium nitrate dissolves in water to form an aqueous solution of ions..

Procedure

Reaction 11. Place 10 mL of water into a test tube cup. Record the temperature of water as

T1.2. QUICKLY measure approximately 0.20 g of NaOH and add it to the water stirring

gently until the pellets have dissolved.3. Record the highest temperature reached as T2.4. Flush the solution down the sink and rinse the cup and thermometer.

Reaction 21. Measure 5 mL of 1.0 M HCl into a test tube.2. Obtain an equal volume of 1.0 M sodium hydroxide in another test tube.3. Record the temperature either solution.4. Pour the NaOH solution into the HCl. Stir and record the highest temperature

reached as T2.5. Discard the solution and clean all materials by rinsing with water.

Reaction 31. Place 10 mL of water into a test tube cup. Record the temperature of water as

T1.2. QUICKLY measure approximately 0.20 g of ammonium nitrate and add it to the

water stirring gently until the pellets have dissolved.3. Record the highest temperature reached as T2.4. Flush the solution down the sink and rinse the cup and thermometer.

Data Table

Reaction Total volume of water used.

Mass of water used. (should be the same!)

Tinitial Tfinal ∆T (final – initial)

q (heat absorbed or released by water.) What sign should you use? What units!

123

Calculations Table

Reaction ∆Hrxn Mass (g) Moles (of each from previous column)

∆Hrxn (in

kJ/mol)

Was the reaction endo or exothermic?

1 Mass of NaOH

2 Mass of NaOH

3 Mass of NH4NO3

1. Draw an energy coordinate diagram for reaction #1.

2. Re-write the reaction for reaction #3 but include the energy in the equation on the correct side.

The Specific Heat of a Metal Experiment

Purpose:To Determine the Specific Heat of a Metal

Equipment Needed: Hot plate, two beakers, Styrofoam cup, string, 100-ml graduated cylinder, electronic balance, thermometer, water, and metal object(s)

Procedure:1. Put on your goggles!2. Measure and record the mass of the metal object in the data table. Attach a piece of string about 15 cm long to the metal object.3. Fill a 250-ml beaker about half-full with water. Place the metal object into the beaker of water with some string protruding over the beaker's lip.4. Place the beaker on the hot plate and allow the water to come to a rolling boil. Allow the metal object to remain in the boiling water for at least five minutes.5. Record the temperature of the boiling water. This will be the initial temperature of the metal object.6. Use a graduated cylinder to pour 100 ml of tap water into the Styrofoam cup. Since the density of water is 1.0 g/ml, record this mass in the data table. For support, place the cup inside a second 250-ml beaker.7. Measure and record the initial temperature of the tap water in the Styrofoam cup.8. Use the protruding string to remove the metal object from the boiling water and quickly lower it into the water in the Styrofoam cup. When the temperature reaches a constant, record it. This will be the final temperature of the metal object and the water.9. Repeat the above procedure for a second trial.

Data Table:

System Surroundings

Data Table

System Surroundings

Calculations:a) Determine the specific heat of your metal by using:

Heat lost by the metal object = Heat gained by the watermmetal cmetal ∆T = mwater cwater ∆T

Trial 1 Calculations

Trial 2 Calculations

b) Determine the Percentage error by using:Percent. Error = (Experimental value - Theoretical value) X 100 %

(Theoretical value)