Energy in systems (thermal, chemical, electrical) Transitional Reasoning Practice

Questions

1. 1.

   A sealed, thermally insulated reaction vessel contains a liquid chemical mixture. An electric heating element submerged in the mixture delivers 75 kJ of electrical energy to drive a reaction process. Diagnostic sensors record that the contents of the vessel experience a total thermal energy increase of 92 kJ over the monitoring interval. Assuming no energy is exchanged across the vessel walls, which statement correctly identifies the chemical energy transformation and its magnitude?

   • A) The reaction is endothermic, and the chemical potential energy of the mixture increased by 17 kJ.
   • B) The reaction is endothermic, and the chemical potential energy of the mixture increased by 167 kJ.
   • C) The reaction is exothermic, and the chemical potential energy of the mixture decreased by 167 kJ.
   • D) The reaction is exothermic, and the chemical potential energy of the mixture decreased by 17 kJ.
2. 2.

   A grid-scale battery pack undergoes testing through a complete charge-discharge cycle that returns it to its initial chemical state. During the charging phase, an external power supply delivers 50.0 MJ of electrical energy to the pack, while internal resistance causes 4.5 MJ of thermal energy to be dissipated into the cooling system. In the subsequent discharge phase, the pack delivers 38.0 MJ of electrical energy to an external circuit. Assuming all non-electrical energy losses are released as thermal energy, how much thermal energy does the battery pack dissipate during the discharge phase alone?

   • A) 3.0 MJ
   • B) 4.5 MJ
   • C) 12.0 MJ
   • D) 7.5 MJ
3. 3.

   An industrial fluid-heating system utilizes both an electric heating element and an exothermic chemical reaction chamber to warm a liquid stream. Over an operating period of 200 seconds, the electric heating element draws a constant electrical power of 1.5 kW, while the chemical chamber consumes reactants that release 180 kJ of stored chemical potential energy as thermal energy. If the liquid stream absorbs 415 kJ of thermal energy during this period and no other energy sources are present, how much thermal energy was dissipated from the system to the surroundings?

   • A) 115 kJ
   • B) 85 kJ
   • C) 65 kJ
   • D) 45 kJ
4. 4.

   An electrochemical cell is operated in a laboratory to synthesize a chemical fuel. During a monitored operating interval, an external power supply delivers 120 kJ of electrical energy to the cell, while diagnostic sensors confirm that the chemical potential energy stored in the synthesized products increases by 145 kJ. Assuming the cell maintains a constant temperature by interacting with its environment, which deduction correctly explains this outcome based on the conservation of energy?

   • A) The electrochemical cell operated with an energy efficiency greater than 100%, allowing electrical energy to multiply spontaneously.
   • B) The cell absorbed thermal energy from its surroundings, converting both thermal and electrical energy into stored chemical potential energy.
   • C) The reaction released thermal energy to the surroundings, which caused the chemical potential energy of the products to increase.
   • D) The electrical resistance of the electrodes converted internal chemical potential energy into additional electrical work.
5. 5.

   A combined heat and power unit utilizes an internal fuel cell to supply both electricity and heating for a research station. Over a steady 10-minute operating interval, the unit consumes fuel supplying 48 MJ of chemical potential energy while delivering electrical power at a constant rate of 35 kW. During the same interval, an integrated heat exchanger successfully captures 18 MJ of thermal energy from the exhaust stream for space heating. Assuming the unit operates in a thermal steady state with no internal energy accumulation, how much thermal energy is dissipated to the surrounding environment during this period?

   • A) 9 MJ
   • B) 12 MJ
   • C) 21 MJ
   • D) 27 MJ
6. 6.

   A portable cooler employs a thermoelectric module powered by a chemical battery to chill an insulated storage chamber. During an operational cycle, the battery consumes 140 kJ of stored chemical potential energy, delivering 120 kJ of electrical energy to the module while dissipating 20 kJ as thermal energy within its own casing. If the module simultaneously extracts 180 kJ of thermal energy from the interior chamber, how much thermal energy is discharged to the surroundings solely by the module's exterior heat sink?

   • A) 60 kJ
   • B) 300 kJ
   • C) 320 kJ
   • D) 180 kJ
7. 7.

   A thermoelectric generator utilizes heat from an alcohol burner to recharge a chemical battery. During a trial, complete combustion of fuel converts 2500 J of chemical potential energy into thermal energy. The generator converts exactly 8% of this thermal energy into electrical energy delivered to the battery, while the rest is lost as heat to the surroundings. If 20 J of the delivered electrical energy is dissipated as thermal energy due to internal resistance while charging, how much chemical potential energy is successfully stored in the battery?

   • A) 180 J
   • B) 200 J
   • C) 220 J
   • D) 2300 J
8. 8.

   An experimental water-electrolysis unit is evaluated to determine how effectively it converts electrical energy into stored fuel. During an operational test, an external power supply delivers 400 kJ of electrical energy to the electrolysis cell. The hydrogen and oxygen gases produced store 290 kJ of chemical potential energy, while temperature sensors record an 85 kJ increase in the thermal energy of the liquid electrolyte. Assuming all energy pathways are accounted for, which statement correctly evaluates energy conservation and distribution in this system?

   • A) The process violates the principle of conservation of energy because 25 kJ of the initial electrical input is permanently destroyed during bond reorganization.
   • B) The liquid electrolyte absorbed 290 kJ of thermal energy, demonstrating that electrical input was primarily degraded rather than converted into chemical potential energy.
   • C) The stored chemical potential energy can exceed the 400 kJ electrical input if the electrolyte spontaneously transfers its 85 kJ of thermal energy back into gas bonds.
   • D) Total energy is strictly conserved across the system boundary, indicating that 25 kJ was transferred to the surrounding environment as thermal energy.
9. 9.

   A benchtop hydrogen fuel cell consumes reactants with 800 J of stored chemical potential energy to power an external electric immersion heater placed in a well-insulated oil bath. High-precision sensors record that the oil bath gains 560 J of thermal energy, while the remaining energy causes a temperature rise in the fuel cell casing. Assuming all electrical energy delivered to the heater is converted into thermal energy in the oil, which statement correctly evaluates the energy pathways and quantities in this system?

   • A) The fuel cell delivered 800 J of electrical energy to the circuit, with 240 J being stored as chemical potential energy in the oil bath.
   • B) The fuel cell dissipated 560 J of thermal energy internally, resulting in only 240 J of electrical energy reaching the immersion heater.
   • C) The fuel cell delivered 560 J of electrical energy to the circuit, while 240 J of the chemical potential energy was converted into thermal energy inside the cell.
   • D) The fuel cell converted all 800 J of chemical potential energy directly into thermal energy, transferring 560 J to the oil bath via electrical conduction.
10. 10.

    An experimental setup consists of an insulated container of water heated by a submerged resistive element connected to a chemical battery. During a testing interval, the battery consumes 180 kJ of stored chemical potential energy, resulting in a measured thermal energy gain of 145 kJ in the water. Assuming no energy is exchanged with the external environment, which statement correctly evaluates the energy pathways and conservation within this system?

    • A) Electrical energy is destroyed in the circuit because only 145 kJ of thermal energy appears in the water from the initial 180 kJ.
    • B) Chemical potential energy converts directly into thermal energy inside the water without generating an intermediate electrical energy pathway.
    • C) Chemical potential energy transforms into electrical energy, which then converts into a total of 180 kJ of thermal energy shared between the water and the internal circuit components.
    • D) Thermal energy increases to 180 kJ in the water because resistive elements generate additional energy beyond the battery's chemical potential energy input.

Answers and step-by-step solutions appear after you finish the test.