chemistry 30 assessment enthalpy change and …

CHEMISTRY 30Assessment

Enthalpy Change andCalorimetry Formative

Record all responses in this book.

Keep this question book and theanswer key as part of your notes.

1. Open and closed systems can be compared by the way matter and energy transfer. How domatter and energy transfer in a closed system?

Matter is transferred, energy is not transferredMatter is not transferred, energy is transferredNeither matter nor energy are transferredBoth matter and energy are transferred

A.B.C.D.

2. The value for an endothermic energy change is positive. This means thatHD

reactants have less potential energy than productsproducts have less potential energy than reactantspotential energy is decreasing in the systemkinetic energy is increasing in the system

A.B.C.D.

3. A common flaw in calorimetry experiments to determine the molar enthalpy of dissolving isto have a mass of solute that is inappropriate for the volume of water used resulting in atemperature change that is too small or too large. A temperature change of 5°C to 10°C isa good range. Calculate the mass of NaOH (molar enthalpy of dissolving is –44.51 kJ/mol )that should be dissolved into 250 mL of water in order to produce a temperature increase of7.00°C.

40.0 g6.59 g4.12 g0.165 g

A.B.C.D.

Chemistry 30 Enthalpy Change and Calorimetry Formative Page 115/09/2014

Use the following information to answer the next two questions

A student using a computer-based laboratory (CBL) temperature probe attempted to determine theamount of energy released by a commerical heat pack. The student activated the heat pack andplaced it in an insulated calorimeter containing 1.00 kg of water at 11.30 °C. A graph of the resultsobtained is given below.

4. To more accurately determine the total heat released by the heat pack, the student should

use more wateruse a larger heat packstart with colder watercollect results for a longer period of time

A.B.C.D.

5. If the energy change of the plastic container is not considered, the calculated energy changefor the water from 0 s to 200 s is

13.0 kJ14.4 kJ60.3 kJ838 kJ

A.B.C.D.


6. In experiments that use a simple calorimeter, the main assumption is that

distilled water is always usedheat is not transferred to the surroundingsthe starting temperature is always room temperaturethe final temperature is always above room temperature

A.B.C.D.

7. The molar enthalpy of neutralization for NaOH(aq) is –59 kJ/mol. In an experiment, 8.0 gof NaOH(s) is dissolved in water and the solution is then allowed to reach roomtemperature. The NaOH(aq) is then added to a strong acid solution which was also initiallyat room temperature. The final volume of solution was 500 mL and the temperatureincreased from 20.0°C to a different temperature. Using this data, what was the finaltemperature of the water?

5.6°C14°C26°C32°C

A.B.C.D.

8. Chromium reacts with oxygen to produce chromium (III) oxide. Which is the correctpotential energy graph for this reaction? Use the standard molar enthalpies of formationtable on page 4 & 5 of your data book to help answer this question.

A. B.

C. D.


9. Use the graph to answer the question.

For the reaction in the potential energy graph above, the reactants have ____i_____potential energy than the products and the reaction is ____ii____ .

The statement above is completed by the information in row

__i__ ____ii____ Less exothermic More exothermic Less endothermic More endothermic

A.B.C.D.

10. Consider the following enthalpy diagram.

The true statement concerning the accompanying diagram is:

is positive.HDthe system is endothermic.the system releases heat to the surroundings.the enthalpy of the products is greater than the enthalpy of reactants.

A.B.C.D.


11. When solid ammonium chloride, NH4Cl, is added to water, the temperature of the solutiondecreases. Which statement best describes this observation?

The reaction is exothermic.NH4Cl (s) does not dissolve in water.NH4Cl (s) + H2O (l) NH4Cl (aq) + 33.6 kJ®

NH4Cl (s) + H2O (l) NH4Cl (aq)® H=+33.6kJD

A.B.C.D.

12. Much of the lead used for batteries and ammunition during the First and Second World Warscame from galena, PbS (s). The following equations represent the reactions that are involvedin refining galena to produce solid lead.

Equation I 2 PbS (s) + 3 O2 (g) 2 PbO (s) + 2 SO2 (g) = -827.4 kJ® HD

Equation II 2 C (S) + O2 (g) 2 CO (g)®

Equation III PbO (s) + CO (g) Pb (s) + CO2 (g)®

In equation I, the reactants have i energy than the products and if energy were included

as a term in the equation, it would be a ii .


__i__ ___ii___ less reactant less product more reactant more product

A.B.C.D.


13. Identify the exothermic reaction

CO (g) + 111 kJ C (s) + O2 (g)® 12

H2 (g) + I2 (g) 2 HI (g) H = +52 kJ® D

2 H2 (g) + O2 (g) 2 H2O H = -486 kJ® D

A.

B.

C.D.

14. When 1.30 mol of HF(g) is dissolved in a large amount of water, the temperature increased

from 20.0°C to 27.6°C. The molar enthalpy of solution for HF(g) is – 61.5 kJ/mol. Fromthe information, what was the mass of water?

9.54 x 102 g

1.49 x 103 g

2.51 x 103 g

5.23 x 103 g

A.B.C.D.


Use the information to answer the next 2 question(s).

A simple calorimeter is made of two nested polystyrene cups. A thermometer, with a mass of22.46 g and a specific heat capacity of 0.865 J/g°C, is used to measure the temperature change.Two solutions are mixed in the calorimeter resulting in a total of 125 mL of water. The increase intemperature recorded was 2.00°C.

15. The quantity of heat absorbed by the thermometer in the above investigation is

1.73°C2.00°C19.4 J38.9 J

A.B.C.D.

16. The error caused by the heat absorbed by the thermometer in the above investigation is

zerotoo small to be measuredusually assumed to be negligibleaccounted for in the calculations in most high school experiments

A.B.C.D.

17. Living plants produce glucose in the process of photosynthesis according to the equationthat follows.

6 CO2 (g) + 6 H2O (l) + energy C6H12O6 (s) + 6 O2 (g)®

This reaction is __ i__ , and the value of is ii .HD


___i __ iiExothermic positiveExothermic negativeEndothermic positiveEndothermic negative

A.B.C.D.

18. Write the chemical equation which best represents the expression that follows.

= –90.8 kJ/mol of mercury (II) oxidef HD

2 Hg (l) + O2 (g) 2 HgO (s) + 90.8 kJ®

2 Hg (l) + O2 (g) + 90.8 kJ 2 HgO (s)®

2 Hg (l) + O2 (g) 2 HgO (s) = –90.8 kJ/mol® f HgOHD

2 Hg (l) + O2 (g) 2 HgO (s) = +90.8 kJ® HD

A.B.C.

D.


For the following numercial response questions, record your answers on the separatenumerical response answer sheet.

1. NUMERICAL RESPONSE

Commercial drain cleaners typically contain sodium hydroxide and aluminum. When the solidcleaner is poured down the drain and water is added, the reaction that occurs is representedby the equation

2 NaOH (s) + 2 Al (s) + 2 H2O (l) 2 NaAlO2 (aq) + 3 H2 (g) = -850.0 kJ® HD

In the production of 4.00 mol of NaAlO2 (aq), the heat released is _______ MJ

(Record your three-digit answer on your response sheet)


Consider the following information.

Calorimetric Data

1 maximum temperature change of water2 mass of aluminum calorimeter3 mass of aluminum calorimeter and water4 initial temperature of aluminum calorimeter5 maximum temperature change of KOH (s)6 mass of KOH (s) used

The data required to determine the molar enthalpy of dissolving for KOH (s), listed innumerical order, are _____, _____, _____ and _____.

(Record your four digit answer in numerical order on your response sheet)



Consider the following reaction:

2 C2H2 (g) + 5 O2 (g) 4 CO2 (g) + 2 H2O (g) = -2 511.0 kJ® HD

The amount of energy released by the combustion of 100 g of C2H2 (g) is _______ MJ



In an experiment, a student heated 500 g of water from 25.0 °C to 91.0 °C using 0.133 mol ofethanol. If it is assumed that all the heat energy was absorbed by the calorimeter water, theexperimental molar enthalpy of combustion for ethanol was +/- ______ MJ/mol.



Consider the following information.

Equations

1 C8H18 (l) + O2 (g) 8 CO2 (g) + 9 H2O (g) + 5 074.1 kJ252

®

2 C3H8 (l) + 5 O2 (g) 3 CO2 (g) + 4 H2O (g) + 2 043. 9 kJ®

3 C2H5OH (l) + 3 O2 (g) 2 CO2 (g) + 3 H2O (g) + 1 234.8 kJ®

4 CH4 (l) + 2 O2 (g) CO2 (g) + 2 H2O (g) + 802.5 kJ®

When ranked in order from the reaction that has the smallest enthalpy change per mole ofcarbon dioxide to the reaction that has the largest enthalpy change per mole of carbondioxide, the reactions are ____, ____, ____ and ____

smallest largest

(Record all four digits of your answer on your response sheet)



A student uses a simple "coffee cup" calorimeter to determine the molar enthalpy of solutionfor solid ammonium nitrate. The experimental evidence collected was recorded below:

Mass of calorimeter 25.45 g Mass of calorimeter and water 175.45 g Mass of ammonium nitrate 1.68 g Initial temperature of water 22.30 oC Final temperature of water 20.98 oC

According to the above data, the molar enthalpy of solution for ammonium nitrateis _______ kJ/mol

(Record your answer to three digits on your response sheet)


Consider the following equation for the combustion of hydrogen:

H2 (g) + O2 (g) H2O (g) + 243 kJ®

In order to produce 1215 kJ of thermal energy _______ g of H2 must be burned.


You have completed the assessment!Please ensure that any separate written response questions are completed.


Chemistry 30 Lesson 1-07 Page 1© 2012 T. de Bruin

Chemistry 30 Enthalpy change & calorimetry formative assessment answer key.

Highlight each question number that was incorrect on your test (Note that a question may apply to more thanone concept). The concept(s) with the most questions highlighted is/are the one(s) that need to be reviewedthoroughly. This is part of your responsibility as a student in this course.

Questions Concept Outcomes

8, 9, 10, 13,17, 18, NR 5

Communicatingenthalpy change

· recall the application of Q = mcDt to the analysis of heat transfer.· explain, in a general way, how stored energy in the chemical bonds

of hydrocarbons originated from the sun.· define enthalpy and molar enthalpy for chemical reactions.· write balanced equations for chemical reactions that include energy

changes.· compare energy changes associated with a variety of chemical

reactions through the analysis of data and energy diagrams.· identify that liquid water and carbon dioxide gas are reactants in

photosynthesis and products of cellular respiration and that gaseouswater and carbon dioxide gas are the products of hydrocarboncombustion in an open system

· classify chemical reactions as endothermic or exothermic, includingthose for the processes of photosynthesis, cellular respiration andhydrocarbon combustion.

2, 12, NR 1,NR 3, NR 7 Enthalpy change

· use and interpret DH notation to communicate and calculate energychanges in chemical reactions.

1, 3, 4, 5, 6, 7,11, 14, 15, 16,NR 2, NR 4,NR 6

calorimetry

· use calorimetry data to determine the enthalpy changes in chemicalreactions

· perform calorimetry experiments to determine the molar enthalpychange of chemical reactions

· use thermometers or temperature probes appropriately whenmeasuring temperature changes


Question Answer Explanation

1 B Basic understanding/definition of open, closed & isolated systems.

2 AEndothermic reactions (positive DH) require an input of energy. This input adds to thepotential energy of the system. Thus endothermic reaction products have morepotential energy than the reactants.

3 B Basic calorimetry calculation using ∆ = ∆ then =

4 D You needed to examine the graph and realize that the temperature had not yetpeaked. Thus the final temperature was taken too early.

5 A Use = ∆

6 B Standard assumptions in calorimetry. The calorimeter is considered to be an isolatedsystem.

7 C Use ∆ = − and solve for

8 DThe DH is negative thus the reaction is exothermic. The enthalpy change graph mustthus go down. This is a formation reaction so the product is written to the right of theenthalpy change arrow in the graph.

9 C If an enthalpy change graph goes up, the reaction is endothermic, absorbing energyand increasing the overall potential energy.

10 C If an enthalpy change graph goes down, the reaction is exothermic releasing energy.

11 D In calorimetry, if the temperature decreases, the chemical reaction/process isabsorbing energy (endothermic).

12 D Equation I has a negative DH, thus the reactants have more potential energy than theproducts. A negative DH is included in a balanced equation as a product.

13 D Choice D is the only negative DH, which is exothermic.

14 C Use ∆ = ∆ and solve for

15 D Use = ∆

16 C Standard assumption in calorimetry that the calorimeter materials absorb/release anegligible amount of energy.

17 C You need to know that photosynthesis is an endothermic process with a positive DH.

18 CA negative DH is exothermic and the value would be included as a product in relationto the amount of moles of the chemical stated. As an enthalpy statement the amountof energy must be in relation to the amount chemical specified.


Question Answer Explanation

NR 1 1.70

Use a ratio to calculate the enthalpy change for a different number of moles:

.

=

Solve for .

You need to note that the answer must be in MJ.

NR 2 1236(any order)

This knowledge was gained from the calorimetry labs. You need to subtract #2 from#3 in order to determine the amount of water in the calorimeter.

NR 3 4.82

Use a ratio to calculate the enthalpy change for a different amount of C2H2:

.

=

. / Solve for .

You need to note that the answer is required to be in MJ.

You could also use ∆ = ∆ = .

= −1255.5 /

then ∆ =. /

− 1255.5 = −4.82

NR 4 1.04 Use ∆ = ∆ and solve for ∆ . You must note that the answer must berecorded as MJ/mol.

NR 5 3124in order

You must calculate ∆ = ∆ for each reaction, where is the number of moles ofCO2 in each balanced equation. Once that is done, rank in order from smallest tolargest.

NR 6 39.5 kJ/mol Use ∆ = ∆ and solve for ∆ . Note the mass of water is calculated bysubtracting the mass of the calorimeter from the mass of the calorimeter and water.

NR 7 10.1 g

Use a ratio to calculate the enthalpy change for a different number of moles:

=

. / Solve for .

You could also use the second method as in NR 3.

chemistry 30 assessment enthalpy change and …

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