6.E: Thermochemistry- Homework
Turn in your answers for the following questions - show your work
- An electric stove has a 1200 watt heating element. If it takes 5 minutes for a teakettle to come to a boil, how much energy (in joules) is required?
- A piece of titanium metal (mass 452.398 g) is placed in boiling water (100.00 °C). After 20 minutes it is removed from the boiling water and placed in a 1.000 liter container of water at 20.00 °C. The temperature of the water increases to 24.28 °C. What is the specific heat of titanium? How does this compare to the value given in the CRC Handbook of Chemistry and Physics?
- Next the same piece of titanium is heated in an acetylene flame (like that used for welding) to an unknown temperature. When the piece of titanium is placed in a 10.000 liter container of water at 20.00 °C the final temperature is now 30.72 °C. What is the temperature of the flame (assuming that the piece of titanium was at equilibrium)? At what temperature does titanium melt?
-
Balance the following reactions, calculate [delta]H
rxn
, calculate the energy released (or required) for the combustion of 10.00 grams of fuel (H
2
, CH
4
(methane), or C
4
H
10
(butane)) in each reaction, and compare the energetics for the reactions (which is the best fuel).
- H 2 (g) + O 2 (g) --> H 2 O (g)
- CH 4 (g) + O 2 (g) --> CO 2 (g) + H 2 O (g)
- C 4 H 10 (g) + O 2 (g) --> CO 2 (g) + H 2 O (g)
The Following Questions are for your practice - Do Not Turn In. They include answers so you can check your work
-
How much heat, in joules and in calories, must be added to a 75.0–g iron block with a specific heat of 0.449 J/g °C to increase its temperature from 25 °C to its melting temperature of 1535 °C?
- answer
-
\(q=mCΔ°T\)
\(q=(75.0g)\times(\dfrac{0.449\:J}{g\:°C})\times(1,510°K) = 50,800J\)
50,800J ; 12,200cal
-
How much would the temperature of 275 g of water increase if 36.5 kJ of heat were added?
- answer
-
ΔT ° = 31.7° C
Calorimetry
-
How much will the temperature of a cup (180 g) of coffee at 95 °C be reduced when a 45 g silver spoon (specific heat 0.24 J/g °C) at 25 °C is placed in the coffee and the two are allowed to reach the same temperature? Assume that the coffee has the same density and specific heat as water.
- answer
-
The temperature of the coffee will drop 1 degree.
-
If a reaction produces 1.506 kJ of heat, which is trapped in 30.0 g of water initially at 26.5 °C in a calorimeter like that in
Figure
, what is the resulting temperature of the water?
- answer
-
38.5 °C
Enthalpy
-
When 2.50 g of methane burns in oxygen, 125 kJ of heat is produced. What is the enthalpy of combustion per mole of methane under these conditions?
- answer
-
802 kJ mol −1
-
Calculate the standard molar enthalpy of formation of NO(
g
) from the following data:
\(\ce{N2}(g)+\ce{2O2}⟶\ce{2NO2}(g)\hspace{20px}ΔH^\circ_{298}=\mathrm{66.4\:kJ}\)
\(\ce{2NO}(g)+\ce{O2}⟶\ce{2NO2}(g)\hspace{20px}ΔH^\circ_{298}=\mathrm{−114.1\:kJ}\)
- answer
-
90.3 mol −1 of NO
-
The decomposition of hydrogen peroxide, H
2
O
2
, has been used to provide thrust in the control jets of various space vehicles. Using the data in
Appendix G
, determine how much heat is produced by the decomposition of exactly 1 mole of H
2
O
2
under standard conditions.
\(\ce{2H2O2}(l)⟶\ce{2H2O}(g)+\ce{O2}(g)\)
- answer
-
−54.04 kJ mol −1
-
Propane, C
3
H
8
, is a hydrocarbon that is commonly used as a fuel.
- Write a balanced equation for the complete combustion of propane gas.
- Assuming that all of the heat released in burning 25.0 grams of propane is transferred to 4.00 kilograms of water, calculate the increase in temperature of the water.
- answer
-
- \(\ce{C3H8}(g)+\ce{5O2}(g)⟶\ce{3CO2}(g)+\ce{4H2O}(l)\);
- 75.4 °C