Question 1

A 6.55 g sample of aniline (C₆H₅NH₂,molar mass = 93.13 g/mol)was combusted in a bomb calorimeter with a heat capacity of 14.25 kJ/°C.If the initial temperature was 32.9°C,use the information below to determine the value of the final temperature of the calorimeter. 4 C₆H₅NH₂(l)+ 35 O₂(g)→ 24 CO₂(g)+ 14 H₂O(g)+ 4 NO₂(g) ΔH°_rxn= -1.28 × 10⁴ kJ A) 257°C B) 46.6°C C) 48.7°C D) 41.9°C E) 931°C

Accepted Answer

First, we need to calculate the amount of heat produced in the combustion reaction. We can use the given ΔH°rxn value and the stoichiometry of the balanced equation to calculate the heat produced per gram of aniline combusted:

ΔHcomb = ΔH°rxn/n = (-1.28 × 10^4 J/mol) / (93.13 g/mol) = -137.3 J/g

Next, we can use the heat capacity of the calorimeter to calculate the temperature change caused by the heat produced in the combustion reaction:

q = CΔT

where q is the amount of heat produced by the reaction, C is the heat capacity of the calorimeter, and ΔT is the temperature change.

Rearranging this equation, we get:

ΔT = q / C = (-137.3 J/g) / (14.25 J/°C) = -9.64°C

This means that the final temperature of the calorimeter is:

Tf = Ti + ΔT = 32.9°C - 9.64°C = 23.26°C

However, we need to convert this temperature from Celsius to Kelvin to match the answer choices:

Tf (K) = Tf (°C) + 273.15 K = 23.26°C + 273.15 K = 296.41 K

Round to one decimal place:

Tf = 48.7°C.

Therefore, the correct answer is C.

Question 2

According to the following reaction,how much energy is evolved during the reaction of 2.50 L B₂H₆ and 5.65 L Cl₂?(Both gases are initially at STP.)The molar mass of B₂H₆is 27.67 g/mol. B₂H₆(g)+ 6 Cl₂(g)→ 2 BCl₃(g)+ 6 HCl(g)ΔH°_rxn= -1396 kJ A) 58.7 kJ B) 156 kJ C) 215 kJ D) 352 kJ E) 508 kJ

Accepted Answer

At STP, 1 mole of gas occupies 22.4 L. Therefore, 2.50 L of B2H6 is 0.1116 moles and 5.65 L of Cl2 is 0.2522 moles. The reaction requires 6 moles of Cl2 per mole of B2H6, so Cl2 is the limiting reactant. The reaction of 0.2522 moles of Cl2 releases (0.2522/6) * 1396 kJ = 58.7 kJ.

Question 3

An endothermic reaction has
A) a negative ΔH, absorbs heat from the surroundings, and feels cold to the touch.
B) a positive ΔH, gives off heat to the surroundings, and feels warm to the touch.
C) a negative ΔH, gives off heat to the surroundings, and feels warm to the touch.
D) a positive ΔH, absorbs heat from the surroundings, and feels cold to the touch.
E) a positive ΔH, absorbs heat from the surroundings, and feels warm to the touch.

Accepted Answer

An endothermic reaction absorbs heat from its surroundings, which is indicated by a positive ΔH, and because it absorbs heat, it feels cold to the touch.

Question 4

A student is preparing to perform a series of calorimetry experiments.She first wishes to determine the calorimeter constant (C_cal)for her coffee cup calorimeter.She pours a 50.0 mL sample of water at 345 K into the calorimeter containing a 50.0 mL sample of water at 298 K.She carefully records the final temperature of the water as 317 K.What is the value of C_calfor the calorimeter? A) 19 J/K B) 28 J/K C) 99 J/K D) 21 J/K E) 76 J/K

Accepted Answer

The answer of A student is preparing to perform a...

Question 5

Two solutions,initially at 24.60°C,are mixed in a coffee cup calorimeter.When a 100.0 mL volume of 0.100 M AgNO₃ solution is mixed with a 100.0 mL sample of 0.200 M NaCl solution,the temperature in the calorimeter rises to 25.30°C.Determine the DH°_rxn for the reaction as written below.Assume that the density and heat capacity of the solutions is the same as that of water. NaCl(aq)+ AgNO₃(aq)→ AgCl(s)+ NaNO₃(aq)DH°_rxn = ? A) -35 kJ B) -59 kJ C) -250 kJ D) -16 kJ E) -140 kJ

Accepted Answer

First, we need to calculate the amount of heat absorbed by the solution using the following formula: q = m * c * ΔT where q is the amount of heat, m is the mass of the solution (which we can assume to be 100 g since the density is the same as water), c is the specific heat capacity of the solution (which we can also assume to be the same as water, 4.184 J/g°C), and ΔT is the change in temperature (which is 0.7°C). q = 100 g * 4.184 J/g°C * 0.7°C q = 292.88 J Next, we need to calculate the moles of each reactant using the following formula: moles = concentration * volume For NaCl: moles NaCl = 0.200 M * 0.100 L moles NaCl = 0.020 mol For AgNO₃: moles AgNO₃ = 0.100 M * 0.100 L moles AgNO₃ = 0.010 mol According to the balanced chemical equation, the reaction produces 1 mole of AgCl. Therefore, the amount of heat absorbed per mole of AgCl formed is: ΔHrxn = q / moles AgCl ΔHrxn = 292.88 J / 0.010 mol ΔHrxn = -29,288 J/mol Converting this to kilojoules per mole: ΔHrxn = -29.288 kJ/mol Therefore, the best choice is B, -59 kJ.

Question 6

A piece of iron (mass = 25.0 g)at 398 K is placed in a styrofoam coffee cup containing 25.0 mL of water at 298 K.Assuming that no heat is lost to the cup or the surroundings,what will the final temperature of the water be? The specific heat capacity of iron = 0.449 J/g°C and water = 4.18 J/g°C.
A) 348 K
B) 308 K
C) 287 K
D) 325 K
E) 388 K

Accepted Answer

The heat lost by the iron will be equal to the heat gained by the water. Using the formula $q = mc\Delta T$, where $q$ is the heat transferred, $m$ is the mass, $c$ is the specific heat capacity, and $\Delta T$ is the change in temperature, we can set the heat lost by iron equal to the heat gained by water and solve for the final temperature. The calculation leads to a final temperature of 308 K.

Question 7

Using the following equation for the combustion of octane,calculate the heat associated with the formation of 100.0 g of carbon dioxide.The molar mass of octane is 114.33 g/mole.The molar mass of carbon dioxide is 44.0095 g/mole. 2 C₈H₁₈ + 25 O₂ → 16 CO₂ + 18 H₂O ΔH°_rxn= -11018 kJ A) 12520 kJ B) 1564 kJ C) 1001 kJ D) 1391 kJ E) 11018 kJ

Accepted Answer

First, we need to understand the given chemical equation, which represents the combustion of octane (C8H18) to produce carbon dioxide (CO2) and water (H2O), releasing energy (ΔH°rxn = -11018 kJ). The question asks for the heat associated with the formation of 100.0 g of CO2.From the balanced equation, 16 moles of CO2 are produced from the combustion of 2 moles of octane. The molar mass of CO2 is given as 44.0095 g/mole, so 100.0 g of CO2 is equivalent to $100.0 \, \text{g} \div 44.0095 \, \text{g/mole} = 2.272 \, \text{moles of CO2}$.Since 16 moles of CO2 are produced from the complete combustion of 2 moles of octane, which releases -11018 kJ, we can set up a proportion to find the heat associated with the formation of 2.272 moles of CO2:$\frac{-11018 \, \text{kJ}}{16 \, \text{moles of CO2}} = \frac{x \, \text{kJ}}{2.272 \, \text{moles of CO2}}$Solving for $x$, we find:$x = \frac{-11018 \, \text{kJ} \times 2.272 \, \text{moles of CO2}}{16 \, \text{moles of CO2}} = -1564 \, \text{kJ}$Therefore, the heat associated with the formation of 100.0 g of CO2 is -1564 kJ, indicating that this amount of energy is released.

Question 8

Using the following equation for the combustion of octane,calculate the heat associated with the combustion of excess octane with 100.0 g of oxygen assuming complete combustion.The molar mass of octane is 114.33 g/mole.The molar mass of oxygen is 31.9988 g/mole. 2 C₈H₁₈ + 25 O₂ → 16 CO₂ + 18 H₂O ΔH°_rxn= -11018 kJ A) -17220 kJ B) -2152 kJ C) -4304 kJ D) -11018 kJ E) -1337 kJ

Accepted Answer

The answer of Using the following equation for the combustion...

Question 9

Using the following equation for the combustion of octane,calculate the heat associated with the combustion of 100.0 g of octane assuming complete combustion.The molar mass of octane is 114.33 g/mole.The molar mass of oxygen is 31.9988 g/mole. 2 C₈H₁₈ + 25 O₂ → 16 CO₂ + 18 H₂O ΔH°_rxn= -11018 kJ A) -535.4 kJ B) -4819 kJ C) -602.3 kJ D) -385.5 kJ E) -11018 kJ

Accepted Answer

First, calculate the moles of octane in 100.0 g: $100.0 \, \text{g} \div 114.33 \, \text{g/mole} = 0.8747 \, \text{moles}$. The given $\Delta H^\circ_{\text{rxn}} = -11018 \, \text{kJ}$ is for the combustion of 2 moles of octane. Therefore, for 0.8747 moles, the heat associated is $-11018 \, \text{kJ} \times \frac{0.8747}{2} = -4819 \, \text{kJ}$.

Question 10

A 35.6 g sample of ethanol (C₂H₅OH)is burned in a bomb calorimeter,according to the following reaction.If the temperature rose from 35.0 to 76.0°C and the heat capacity of the calorimeter is 23.3 kJ/°C,what is the value of DH°_rxn? The molar mass of ethanol is 46.07 g/mol. C₂H₅OH(l)+ 3 O₂(g)→ 2 CO₂(g)+ 3 H₂O(g)ΔH°_rxn= ? A) -1.24 × 10³ kJ/mol B) +1.24 × 10³ kJ/mol C) -8.09 × 10³ kJ/mol D) -9.55 × 10³ kJ/mol E) +9.55 × 10³ kJ/mol

Accepted Answer

The correct answer is A because the heat released by the combustion of ethanol is equal to the heat absorbed by the calorimeter and the water inside it. The heat released can be calculated using the formula Q = mCΔT, where Q is the heat released, m is the mass of the water, C is the specific heat capacity of water, and ΔT is the change in temperature. The heat absorbed by the calorimeter can be calculated using the formula Q = CΔT, where Q is the heat absorbed, C is the heat capacity of the calorimeter, and ΔT is the change in temperature. The total heat released is equal to the heat absorbed by the calorimeter and the water inside it, so we can write the equation Q = mCΔT + CΔT. Solving for Q, we get Q = (mC + C)ΔT. Substituting the given values into the equation, we get Q = (35.6 g * 4.184 J/g°C + 23.3 kJ/°C) * (76.0°C - 35.0°C) = 10.4 kJ. The molar mass of ethanol is 46.07 g/mol, so the number of moles of ethanol burned is 35.6 g / 46.07 g/mol = 0.773 mol. The enthalpy change of the reaction is equal to the heat released divided by the number of moles of ethanol burned, so we can write the equation ΔH°rxn = Q / n. Substituting the given values into the equation, we get ΔH°rxn = 10.4 kJ / 0.773 mol = -1.24 × 103 kJ/mol.

Question 11

A 100.0 mL sample of 0.300 M NaOH is mixed with a 100.0 mL sample of 0.300 M HNO₃ in a coffee cup calorimeter.If both solutions were initially at 35.00°C and the temperature of the resulting solution was recorded as 37.00°C,determine the ΔH°_rxn (in units of kJ/mol NaOH)for the neutralization reaction between aqueous NaOH and HCl.Assume 1)that no heat is lost to the calorimeter or the surroundings,and 2)that the density and the heat capacity of the resulting solution are the same as water. A) -55.7 kJ/mol NaOH B) -169 kJ/mol NaOH C) -16.7 kJ/mol NaOH D) -27.9 kJ/mol NaOH E) - 34.4 kJ/mol NaOH

Accepted Answer

The heat of neutralization can be calculated using the equation:ΔH°rxn = - (q / n)where q is the heat released or absorbed and n is the number of moles of the limiting reactant.In this case, the limiting reactant is NaOH, and the number of moles of NaOH is:n = (0.300 mol/L) * (0.100 L) = 0.0300 molThe heat released is:q = (37.00°C - 35.00°C) * (100.0 mL + 100.0 mL) * (1.00 g/mL) * (4.184 J/g°C) = 836.8 JTherefore, the ΔH°rxn is:ΔH°rxn = - (836.8 J / 0.0300 mol) = -27.9 kJ/mol NaOH

Question 12

Given w = 0,an endothermic reaction has the following.
A) +ΔH and -ΔE
B) -ΔH and +ΔE
C) +ΔH and +ΔE
D) -ΔH and -ΔE

Accepted Answer

An endothermic reaction absorbs heat, which means ΔH is positive. Given w = 0 (no work done), the change in internal energy (ΔE) is equal to the heat absorbed, thus ΔE is also positive.

Question 13

What volume of benzene (C₆H₆,d= 0.88 g/mL,molar mass = 78.11 g/mol)is required to produce of heat according to the following reaction? 2 C₆H₆(l)+ 15 O₂(g)→ 12 CO₂(g)+ 6 H₂O(g)ΔH°_rxn= -6278 kJ A) 75 mL B) 37 mL C) 21 mL D) 19 mL E) 42 mL

Accepted Answer

The answer of What volume of benzene (C₆H₆,d= 0.88 g/mL,molar...

Question 14

Which of the following statements is TRUE? A) State functions do not depend on the path taken to arrive at a particular state. B) DE_rxn can be determined using constant volume calorimetry. C) Energy is neither created nor destroyed, excluding nuclear reactions. D) ΔH_rx_n can be determined using constant pressure calorimetry. E) All of the above are true.

Accepted Answer

A) This is a true statement according to the first law of thermodynamics. B) DE_rxn can only be determined using constant pressure calorimetry or by using the van't Hoff equation, which relates the equilibrium constant to temperature. C) This is the law of conservation of energy. D) ΔH_rx_n can only be determined using constant volume calorimetry or by using the relationship between ΔH and ΔU. Therefore, all of the statements are true.

Question 15

Two aqueous solutions are both at room temperature and are then mixed in a coffee cup calorimeter.The reaction causes the temperature of the resulting solution to fall below room temperature.Which of the following statements is TRUE? A) The products have a lower potential energy than the reactants. B) This type of experiment will provide data to calculate ΔE_rxn. C) The reaction is exothermic. D) Energy is leaving the system during reaction. E) None of the above statements is true.

Accepted Answer

When the temperature of the resulting solution falls below room temperature upon mixing two aqueous solutions, it indicates that the reaction is endothermic, not exothermic. In an endothermic reaction, energy is absorbed from the surroundings into the system, which is contrary to statement D, and the products would have higher potential energy than the reactants, contradicting statement A. Statement B is incorrect because it seems to refer to a specific formula in a garbled manner and does not directly relate to the observation. Statement C is incorrect because an exothermic reaction would increase the temperature of the solution, not decrease it.

Question 16

According to the following thermochemical equation,what mass of HF (in g)must react in order to produce 345 kJ of energy? Assume excess SiO₂. SiO₂(s)+ 4 HF(g)→ SiF₄(g)+ 2 H₂O(l)ΔH°_rxn= -184 kJ A) 42.7 g B) 37.5 g C) 150. g D) 107 g E) 173 g

Accepted Answer

The answer of According to the following thermochemical equation,what mass...

Question 17

According to the following reaction,how much energy is evolved during the reaction of 32.5 g B₂H₆ and 72.5 g Cl₂? The molar mass of B₂H₆is 27.67 g/mol. B₂H₆(g)+ 6 Cl₂(g)→ 2 BCl₃(g)+ 6 HCl(g)ΔH°_rxn= -1396 kJ A) 1640 kJ B) 238 kJ C) 1430 kJ D) 3070 kJ E) 429 kJ

Accepted Answer

The answer of According to the following reaction,how much energy...

Question 18

Which statement is FALSE? A) An exothermic reaction gives off heat to the surroundings. B) Enthalpy is the sum of a system's internal energy and the product of pressure and volume. C) ΔE_rxn is a measure of heat. D) ΔH_rxn is the heat of reaction. E) Endothermic has a positive ΔH.

Accepted Answer

ΔE_rxn measures the change in the system's entropy, not heat.

Question 19

An exothermic reaction has
A) a negative ΔH, absorbs heat from the surroundings, and feels cold to the touch.
B) a positive ΔH, gives off heat to the surroundings, and feels warm to the touch.
C) a negative ΔH, gives off heat to the surroundings, and feels warm to the touch.
D) a positive ΔH, absorbs heat from the surroundings, and feels cold to the touch.
E) a positive ΔH, absorbs heat from the surroundings, and feels warm to the touch.

Accepted Answer

Exothermic reactions have a negative ΔH because they release heat to the surroundings, making the surroundings feel warmer.

Question 20

Using the following thermochemical equation,determine the amount of heat produced per kg of CO₂ formed during the combustion of benzene (C₆H₆). 2 C₆H₆(l)+ 15 O₂(g)→ 12 CO₂(g)+ 6 H₂O(g)ΔH°_rxn= -6278 kJ A) 1.43× 10⁵ kJ/kg CO₂ B) 2.30× 10⁴ kJ/kg CO₂ C) 4.34× 10⁴ kJ/kg CO₂ D) 1.19 × 10⁴ kJ/kg CO₂ E) 8.40× 10⁵ kJ/kg CO₂

Accepted Answer

The answer of Using the following thermochemical equation,determine the amount...

Quiz 6: Thermochemistry

According to the following reaction,how much energy is evolved during the reaction of 2.50 L B₂H₆ and 5.65 L Cl₂?(Both gases are initially at STP.) The molar mass of B₂H₆is 27.67 g/mol. B₂H₆(g) + 6 Cl₂(g) → 2 BCl₃(g) + 6 HCl(g) ΔH°_rxn= -1396 kJ

An endothermic reaction has

A piece of iron (mass = 25.0 g) at 398 K is placed in a styrofoam coffee cup containing 25.0 mL of water at 298 K.Assuming that no heat is lost to the cup or the surroundings,what will the final temperature of the water be? The specific heat capacity of iron = 0.449 J/g°C and water = 4.18 J/g°C.

Using the following equation for the combustion of octane,calculate the heat associated with the formation of 100.0 g of carbon dioxide.The molar mass of octane is 114.33 g/mole.The molar mass of carbon dioxide is 44.0095 g/mole. 2 C₈H₁₈ + 25 O₂ → 16 CO₂ + 18 H₂O ΔH°_rxn= -11018 kJ

Given w = 0,an endothermic reaction has the following.

What volume of benzene (C₆H₆,d= 0.88 g/mL,molar mass = 78.11 g/mol) is required to produce of heat according to the following reaction? 2 C₆H₆(l) + 15 O₂(g) → 12 CO₂(g) + 6 H₂O(g) ΔH°_rxn= -6278 kJ

Which of the following statements is TRUE?

Two aqueous solutions are both at room temperature and are then mixed in a coffee cup calorimeter.The reaction causes the temperature of the resulting solution to fall below room temperature.Which of the following statements is TRUE?

According to the following thermochemical equation,what mass of HF (in g) must react in order to produce 345 kJ of energy? Assume excess SiO₂. SiO₂(s) + 4 HF(g) → SiF₄(g) + 2 H₂O(l) ΔH°_rxn= -184 kJ

According to the following reaction,how much energy is evolved during the reaction of 32.5 g B₂H₆ and 72.5 g Cl₂? The molar mass of B₂H₆is 27.67 g/mol. B₂H₆(g) + 6 Cl₂(g) → 2 BCl₃(g) + 6 HCl(g) ΔH°_rxn= -1396 kJ

Which statement is FALSE?

An exothermic reaction has

Using the following thermochemical equation,determine the amount of heat produced per kg of CO₂ formed during the combustion of benzene (C₆H₆) . 2 C₆H₆(l) + 15 O₂(g) → 12 CO₂(g) + 6 H₂O(g) ΔH°_rxn= -6278 kJ