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
Q5.1.6
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?
S5.1.6
\(q=mCΔ°T\)
\(q=(75.0g)\times(\dfrac{0.449\:J}{g\:°C})\times(1,510°K) = 50,800J\)
50,800J ; 12,200cal
Q5.1.8
How much would the temperature of 275 g of water increase if 36.5 kJ of heat were added?
S5.1.8
ΔT ° = 31.7° C
Calorimetry
Q5.2.6
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.
S5.2.6
The temperature of the coffee will drop 1 degree.
Q5.2.9
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?
S5.2.9
38.5 °C
Enthalpy
Q5.3.10
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?
S5.3.10
802 kJ mol −1
Q5.3.28
Calculate the standard molar enthalpy of formation of NO( g ) from the following data:
\(\ce{N2}(g)+\ce{2O2}⟶\ce{2NO2}(g)\hspace{20px}ΔH^\circ_{298}=\mathrm{66.4\:kJ}\)
\(\ce{2NO}(g)+\ce{O2}⟶\ce{2NO2}(g)\hspace{20px}ΔH^\circ_{298}=\mathrm{−114.1\:kJ}\)
S5.3.28
90.3 mol −1 of NO
Q5.3.32
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.
\(\ce{2H2O2}(l)⟶\ce{2H2O}(g)+\ce{O2}(g)\)
S5.3.32
−54.04 kJ mol −1
Q5.3.45
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.
S5.3.45
- \(\ce{C3H8}(g)+\ce{5O2}(g)⟶\ce{3CO2}(g)+\ce{4H2O}(l)\);
- 75.4 °C