6. What quantity, in moles,of hydrogen is consumed when 1S1.1 kJ of energy is ev
ID: 693355 • Letter: 6
Question
6. What quantity, in moles,of hydrogen is consumed when 1S1.1 kJ of energy is evolved from the combustion of a mixture of H2(g) and 0 (8)? a. 0.5286 mol b.0.2643 mol c. 1.891 mol d. 1.528 mol e. 0.4713 mol 7. One statement of the first law of thermodynamics is that a. the amount of work done on a system is dependent of the pathway b. the total work done on a system must equal the heat absorbed by the system. work done on a system is equal in magnitude, but opposite in sign of the heat absorbed by the system d. the total energy change for a system is equal to the sum of the heat transferred to or from the system and the work done by or on the system. e. in any chemical process the heat flow must equal the change in enthalpy 8. When 10.0 g KOH is dissolved in 100.0 g of water in a coffee-cup calorimeter, the temperature rises from 25.IS C to 47.53 °C. What is the enthalpy change per gram of KOH dissolved in the water? Assume that the solution has a specific heat capacity of 4.18 J/g.K a. -116 Jg b.-934 J/g e.-103 x 103Jg d.-2.19 x to3Jg e. -1.03 x 104/g 9. What is the energy per mole of photons of light with a frequency of 6.39 x 1013 Hz? a. 3.11 x 10-30 kJ/mol b. 2.55 x 10' /mo c. 2.83 x 1024 kJ/mol d. 1.87 x 10-9 k/mol e. 4.7× 103 klinol 10. Which of the following is an endothermic process? a. work is done by the system on the surroundings b. heat energy flows from the system to the surroundings c. work is done on the system by the surroundings d. heat energy is evolved by the system e. none of the aboveExplanation / Answer
Q6.
H2 + 1/2 O2 ----------> H2O
Heat of reaction is - 285.8kJ/mol
It means - 285.8kJ/mol of energy is released when 1 mole of H2 is combsted. The two figures can be equated as
- 285.8kJ/mol = 1 mole of H2
If 1 kJ of energy is released ,, then moles of H2 combustd is given as
1kJ = 1 mole of H2 / - 285.8kJ = 0.0035 moles of H2.
Hence an energy of 151.1 kJ means 151.1 X 0.0035 = 0.5286 moles of H2 are combusted. Hence option (a) is correct answer.
Q7. Option (d) is correct. It is mathemetically shown as
U = w + q
U = energy change of the system
w = energy exchange as work , q = heat exchange
Q8..
Energy released = - mcT , minus sign indicates energy is released.
m = mass of the system = 100g (water) + 10g (KOH) = 110g , c = specific heat = 4.18J/g K,
T = temperature change = 320.53 K = 298.18 K = 22.35K
Energy released = - 110 X 4.18 X 22.35 = 10275.53 J
Energy released per gram of KOH=Total energy change/mass of KOH = - 10275.53 J / 10g = 1027.55 J/g = 1.03 kJ
Hence option (c) is correct answer.
Q9
Energy of the photon = hv = 6.6 X 10-34Js X 6.39 X 1013 Hz = 42.2 X 10-21J
Energy of one mole of photon = Energy of one photo X Avagadro constant (6.23 X 1023)
Energy of one mole of photon = 42.2 X 10-21J X 6.23 X 1023 = 2.6 X 104J/mol = 2.6 X 101 kJ/mol
Hence option (b) is correct answer.
Q10. Option (e) is correct answer.
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