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Exam 6: Thermochemistry

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Question 31

Multiple Choice

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A piece of iron (C = 0.449 J/g°C) and a piece of gold (C = 0.128 J/g°C) have identical masses.If the iron has an initial temperature of 498 K and the gold has an initial temperature of 298 K,which of the following statements is TRUE of the outcome when the two metals are placed in contact with one another? Assume no heat is lost to the surroundings.

A) Since the two metals have the same mass,the final temperature of the two metals will be 398 K,exactly half way in between the two initial temperatures.
B) Since the two metals have the same mass,but the specific heat capacity of gold is much smaller than that of iron,the final temperature of the two metals will be closer to 298 K than to 498 K.
C) Since the two metals have the same mass,the thermal energy contained in the iron and gold after reaching thermal equilibrium will be the same.
D) Since the two metals have the same mass,but the specific heat capacity of iron is much greater than that of gold,the final temperature of the two metals will be closer to 498 K than to 298 K.
E) None of the above are true.

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Question 32

Multiple Choice

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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 ΔH°_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

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Question 33

Multiple Choice

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The specific heat capacity of liquid mercury is 0.14 J/g ∙ K.How many joules of heat are needed to raise the temperature of 5.00 g of mercury from 15.0°C to 36.5°C?

Energy that is associated with the position or composition of an object is called

When 10.00 moles of H₂(g) reacts with 5.000 mol of O₂(g) to form 10.00 mol of H₂O(l) at 25°C and a constant pressure of 1.00 atm.If 683.0 kJ of heat are released during this reaction,and PΔV is equal to -37.00 kJ,then

Define chemical energy.

Match the following. -+w

Calculate the change internal energy (ΔE) for a system that is giving off 45.0 kJ of heat and is performing 855 J of work on the surroundings.

Match the following. -+q

For a process at constant pressure,49,600 calories of heat are released.This quantity of heat is equivalent to

Use the ΔH°_f and ΔH°_rxn information provided to calculate ΔH°_f for SO₃(g) : ΔH°_{f (kJ/mol)} 2 SO₂(g) + O₂(g) → 2 SO₃(g) ΔH°_rxn = -198 kJ SO₂(g) -297

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 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.

Calculate the change in internal energy (ΔE) for a system that is absorbing 35.8 kJ of heat and is expanding from 8.00 to 24.0 L in volume at 1.00 atm.(Remember that 101.3 J = 1 L^∙atm)

Use the standard reaction enthalpies given below to determine ΔH°_rxn for the following reaction: P₄(g) + 10 Cl₂(g) → 4PCl₅(s) ΔH°_rxn = ? Given: PCl₅(s) → PCl₃(g) + Cl₂(g) ΔH°_rxn= +157 kJ P₄(g) + 6 Cl₂(g) → 4 PCl₃(g) ΔH°_rxn = -1207 kJ

What is the enthalpy change (in kJ) of a chemical reaction that raises the temperature of 250.0 ml of solution having a density of 1.25 g/ml by 7.80°C? (The specific heat of the solution is 3.74 j/g ∙ K. )

When 1.50 g of Ba(s) is added to 100.00 g of water in a container open to the atmosphere,the reaction shown below occurs and the temperature of the resulting solution rises from 22.00°C to 33.10°C.If the specific heat of the solution is 4.18 J/(g ∙ °C) ,calculate ΔH for the reaction,as written. Ba(s) + 2 H₂O(l) → Ba(OH) ₂(aq) + H₂(g) ΔH = ?

Why are the standard heats of formation for elements in their most stable form assigned a value of "0"?

A sample of copper absorbs 43.6 kJ of heat,resulting in a temperature rise of 75.0°C,determine the mass (in kg) of the copper sample if the specific heat capacity of copper is 0.385 J/g°C.

Determine the specific heat capacity of an alloy that requires 59.3 kJ to raise the temperature of 150.0 g alloy from 298 K to 398 K.