Unit Test: 4.13 Unit Test: Chemical Thermodynamics

If 4.5 kJ of energy is added to 100 g of copper at 100ºC, what is the final temperature in degrees Celsius?

215

In a calorimeter, 6.68 kJ of heat was absorbed by 20 g of ice. What is the enthalpy of fusion of the ice? q=mΔHf

334 J/g

In a calorimeter, 1.0 kg of ice melts at 0oC. The enthalpy of fusion of the ice is 334 J/g. (Hint: Use q=mHf Also, be careful with units. Your intial mass may need to be converted to g and then your answer for q, may need to be converted!) How much heat was absorbed?

334 kJ

Which statement is a correctly written thermochemical equation?

4Fe (s) + 3O2 (g)→2Fe2O3 (s), ΔH = −3,926 kJ

How much ethanol freezes to release 25 kJ of heat (△Hf=4.60 kJ/mol) ?

5.45 mol

A chemical reaction is carried out in a closed container. The energy absorbed by the chemical reaction is 50 kJ. What is the energy liberated from the air or the walls of the container?

50 kJ

Which statement is true?

In an exothermic reaction, the energy of the products is less than the energy of the reactants.

In which thermochemical equations would the ΔH be considered a heat of solution?

NH4NO3(s)→NH4+(aq)+NO3-(aq), ΔH=+25.7 kJ/mol

Which example is an exothermic reaction?

condensation

Which action has a positive enthalpy without a temperature change?

evaporating a liquid

Two hundred grams of a substance requires 0.52 kJ of heat to raise its temperature from 25°C to 45°C. Use the table to identify the substance. q=mCΔT. Mass (m) is in grams. Temperature is in degrees Celsius.

gold

Which term measures the energy transferred from one object to another?

heat

This diagram would represent the enthalpy changes in which example?

hot pack

Which parameter is kept constant in a coffee-cup calorimeter?

pressure

You have a series of four chemical reactions (1→2→3→4)(1→2→3→4). How do you calculate the ΔH2ΔH2 if you know the other ΔHΔH values? (Hint: this is a Hess's Law problem, where RXN 4 represents the total of the other 3 RXNs)

ΔH2=ΔH4−(ΔH1 + ΔH3)

What is likely to be true about the ∆H for this reaction? C6H6 (l) → C6H6 (s)

∆H<0

How much heat do you need to raise the temperature of 150 g of oxygen from −30 °C to−15 °C ?

2.07 kJ

You have the equations: 2H2O(l)→2H2(g)+O2(g), △H=572 kJ2H2O(l)→2H2(g)+O2(g), △H=572 kJ2N2(g)+3H2(g)→2NH3(g), △H=−138 kJ2N2(g)+3H2(g)→2NH3(g), △H=−138 kJ2NO2(g)+7H2(g)→2NH3(g)+4H2O(l), △H=−1.18×103 kJ2NO2(g)+7H2(g)→2NH3(g)+4H2O(l), △H=−1.18×103 kJ2NO2(g)→2N2(g)+2O2(g), △H=□2NO2(g)→2N2(g)+2O2(g), △H=□ What is the missing △H ?

+99.0 kJ

How much heat is given off when 16 g liquid methanol (CH3OH) at its freezing point changes to solid methanol? (methanol ΔHf=3.16 kJ/mol)

1.58 kJ

The reaction 2NO (g) → N2 (g) + O2 (g) has a ΔH =−180.5 kJ .

180.5 kJ

Two objects (A and B) of the same temperature are in contact with each other. Which statement is true?

Although the molecules collide, no heat transfers because there is no temperature difference between the objects.

Which type of substance would be best for use in a cooling system?

a liquid with a high specific heat

By using the following reactions, calculate the heat of combustion of pentane: C5H12(g)+8O2(g)→5CO2(g)+6H2O(l)C5H12(g)+8O2(g)→5CO2(g)+6H2O(l). C(s)+O2(g)→CO2(g), △H=−395 kJC(s)+O2(g)→CO2(g), △H=−395 kJH2(g)+12O2(g)→H2O(l), △H=−285 kJH2(g)+12O2(g)→H2O(l), △H=−285 kJ5C(s)+6H2(g)→C5H12(g), △H=−147 kJ

−3.54×103 kJ

What is the change in enthalpy when 180 g of water vapor condenses at 100oC? (Hint: use Q=moleHf Also, keep in mind that ΔHv=40.67 kJ/mol represents vaporation and this problem is the inverse, condensation!) (ΔHv=40.67 kJ/mol)

−407 kJ

Consider these equations: 2S (s) + 3O2 (g)→2SO3 (g)2S (s) + 3O2 (g)→2SO3 (g), ΔH = −792 kJΔH = −792 kJ 2S (s) + 2O2 (g)→2SO2 (g)2S (s) + 2O2 (g)→2SO2 (g), ΔH =?ΔH =? 2SO2 (g) + O2 (g)→2SO3 (g)2SO2 (g) + O2 (g)→2SO3 (g), ΔH = −198 kJΔH = −198 kJ What is the missing ΔHΔH?

−594 kJ