Specific Heat
A chunk of 50.0 g iron metal at 150.C is placed in 50.0 mL water at 20.C. The water and metal are allowed to reach equilibrium. The final temperature of the water will be...
a) 85C
b) more than 85C
c) less than 85C
d) impossible to tell
less than 85C
The water gains the same amount of energy as the metal loses, BUT the high specific heat of water allows for less of a change in temperature.
Use BOND ENERGIES to calculate the enthalpy of the following equation
__H2 + __Cl2 --> __HCl
-183 kJ/mol
A chemical reaction is found to be endothermic. This means energy went from...
a) surroundings to system
b) system to surroundings
c) universe to surroundings
d) surroundings to universe
a) surroundings to system - by definition, endothermic reactions take energy in.
Determine enthalpy in kJ for the following reaction using the listed enthalpies of reaction:
N2H4(l) + 2 H2O2(g)→ N2(g) + 4 H2O(l)
N2H4(l) + O2(g) →N2(g) + 2 H2O(l) ΔH = -622.3 kJ
H2(g) + 1/2 O2(g) → H2O(l) ΔH = -285.8 kJ
H2(g) + O2(g) → H2O2(g) ΔH = -187.8 kJ
-818.3 kJ
Which of the following has the greater entropy in each pairing?
CO2 (g) or CO2(s)
C2H4 (g) or C6H14 (g)
Copper at 100 0C or copper at 1000 0C
1. gas
2. C6H14
3. 1000 C
What is the specific heat of a metal which has a mass of 25.0g, a temperature change from 25.0 degrees Celsius to 75.0 degrees Celsius, and absorbed 162.4J of heat?
What is 0.130 J/g°C
Use BOND ENTHALPIES OF FORMATION to determine the enthalpy of reaction
3SO2(g) + 2HNO3(aq) + 2H2O(l) → 3H2SO4(aq) + 2NO(g)
671.5 kJ/mol
How much heat will be released when 25.0 g of carbon reacts with excess O2 according to the following equation?
C + O2 → CO2 ∆H = -393.5 kJ
819 kJ
Given the following equations and Ho values, determine the heat of reaction (kJ) at 298 K for the reaction:
2 OF2(g) + 2 S(s)→ SO2(g) + SF4(g)
OF2(g) + H2O(l) →O2(g) + 2 HF(g) ΔH = -276.6
SF4(g) + 2 H2O(l) → 4 HF(g) + SO2(g) ΔH = -827.5
S(s) + O2(g) → SO2(g) ΔH = -296.9
-319.5 kJ/mol
For a certain process at 300.0 K, ΔG = -77.0 kJ/mol and ΔH = -56.9 kJ/mol. Find the entropy change for this process in J/(molK).
67.0 J/(molK)
A 250.0 g sample of mercury is at 50.0°C. What is the final temperature of the mercury when it absorbs 5.50 kJ of energy? (the specific heat for mercury is 0.140 J/g°C)
207°C
endothermic
What mass of propane, C3H8 must be burned in order to produce 88,000 kJ of energy?
C3H8 + 5O2 → 3CO2 + 4H2O ∆H = -2200 kJ
1800 g
Given the following equations and Ho values, determine the heat of reaction at 298 K for the reaction:
C(s) + 2 H2(g)→ CH4(g)
C(s) + O2(g) → CO2(g) ΔH = -393.5
H2(g) + 1/2 O2(g) → H2O(l) ΔH = -285.8
CO2(g) + 2 H2O(l) → CH4(g) + 2 O2(g) ΔH = +890.3
-74.8 kJ
A student collected the following data during a chemical reaction
ΔH =+12 kJ/mol ΔS =+10. J/(K mol)
What temperature is required to make this reaction spontaneous?
Temperatures higher than 1200 K
In a coffee-cup calorimeter, 50.0 g of H2O and 12.5 g NaCl are mixed. The water was originally at 24.6 C. After the reaction, the temperature of both substances is 35.3 C.
What is the enthalpy of solution for the salt in kJ/mol
10.5 kJ/mol
Use BOND ENTHALPIES to determine the enthalpy of reaction
2C2H6 (g) + 7O2 (g) --> 4CO2 (g) + 6H2O (g)
-2857.2 kJ
What mass of propane, water is produced when 88,000 kJ of energy is released?
C3H8 + 5O2 → 3CO2 + 4H2O ∆H = -2200 kJ
2900 g
What mass of oxygen are needed to give off 8500 kJ of energy according to the following combustion reaction?
C2H2(g) + 5/2O2(g) → 2CO2(g) + H2O(g)
C2H6(g) → C2H2(g) + 2H2(g) ΔH = 283.5 kJ
H2(g) + 1/2O2(g) → H2O(g) ΔH = -213.7 kJ
2CO2(g) + 3H2O(g) → C2H6(g) + 7/2O2(g) ΔH = 849.0 kJ
-705.1 kJ
The vaporization of bromine requires +31.0 kJ/mol and has an increase in disorder (ΔS˚ = 93.0 J/(mol•K)). At what minimum temperature will this process be spontaneous?
Br2 (l) → Br2 (g)
333 K
A piece of metal weighing 59.047 g was heated to 100.0 °C and then put it into 100.0 mL of water (initially at 23.7 °C). The metal and water were allowed to come to an equilibrium temperature, determined to be 27.8 °C. Assuming no heat lost to the environment, calculate the specific heat of the metal.
0.402 J/gC
Given that ∆H°rxn=47.2kJ/mol for the following, calculate the ∆H°f for Fe3O4(s).
2 Fe3O4 (s) + CO2 (g) → 3 Fe2O3 (s) + CO (g)
-1118.4 kJ
How much heat will be released when 20.0 g of H2 reacts with 106.0 g of O2 according to the following equation?
2H2 + O2 → 2H2O ∆H = -571.6 kJ
1893 kJ
15.0 L of O2 gas and excess N2 at STP are used in the following reaction. How much energy is absorbed/released from this reaction?
N2(g) + 2O2(g) → 2NO2(g)
N2(g) + 3H2(g) → 2NH3(g) ΔH = -115.0 kJ
2NH3(g)+4H2O(l)→2NO2(g)+7H2(g) ΔH = -142.5 kJ
H2O(l) → H2(g) + 1/2O 2(g) ΔH = -43.7 kJ
ΔH=-82.7 kJ
BUT the final answer is...27.7 kJ (use stoichiometry)
Methanol (CH3OH) is used as rocket fuel. Look at the reactants and products to analyze.
CH3OH (l) + 3/2 O2 (g) → CO2 (g) + 2 H2O (g)
a.Predict the sign of ΔS
b.Predict the sign of ΔH
c. Is this reaction favorable at high, low, all temperatures, or never favorable?
a) +
b) -(think about the fact it is ROCKET FUEL and combusts!)
c) All temps(don't get this confused with activation energy which this will need a "spark" to get to begin to ignite)