Thermochemistry Questions With Answers

What is frost an example of?

Answer: Deposition Explanation: Frost is an example of a gas changing directly to a solid.

Would the freezing of water be endothermic or exothermic?

Answer: Exothermic Explanation: This would be an exothermic reaction, because the freezing would require the water to lose heat, so that it could change forms from liquid to solid.

Which temperature is equal to 120. K?

Answer: -153 degrees Celsius Explanation: On the back of the Chemistry reference table, there is a chart for converting Kelvin to Celcius and the other way around. For this conversion, you need to take the 120 Kelvin and subtract 273 from it, giving you -153 degrees Celsius.

What value does the heat of fusion equal to?

Answer: 334J/g Explanation: On the Chemistry reference table, the heat of fusion is seen on Table B to equal 334J/g.

According to the Chemistry reference table, what Celsius temperature does Propanone boil at?

Answer: 55 degrees Celsius Explanation: Propanone boils at about 55 degrees Celsius, as seen on Table H of the reference table.

Which temperature represents absolute zero? A. 0 K B. 0 degrees Celsius C. 273 K D. 273 degrees celsius

Answer: A Explanation: Absolute zero equals 0 Kelvin, or 0 K.

The temperature of a sample of matter is a measure of the A. average kinetic energy of its particles. B. average potential energy of its particles C. total kinetic energy of its particles. D. total potential energy of its particles

Answer: A Explanation: The definition of temperature clearly states that it is the average kinetic energy of a substance's particles. None of the other options listed make any sense, or relate to an actual idea.

Which term identifies a form of energy? A. Thermal B. Exothermic C. Combustion D. Electrolytic

Answer: A Explanation: Thermal energy is an actual form of energy, while exothermic and combustion represent types of reactions. Electrolytic is a type of electrical current.

Which physical changes are endothermic? A. melting and freezing B. melting and evaporating C. condensation and sublimation D. condensation and deposition

Answer: B Explanation: Melting and evaporating are both processes that require energy to be absorbed within a substance to occur. Sublimation is also a process which requires heat to be gained by a substance. However, the only choice with two endothermic changes is B.

As electrical energy is converted into heat energy, the total amount of energy in the system A. decreases B. increases C. remains the same

Answer: C Explanation: As stated in the law of Conservation of Energy, energy in a system cannot be created or destroyed.

Which substance will readily sublime at STP? A. Fe(s) B. NaCl(s) C. CO2(s) D. C6H12O6(s)

Answer: C Explanation: CO2(s) is dry ice, which undergoes sublimation when exposed to the atmospheric temperature.

Which is not a type of energy? A. Sound B. Wind C. Combustion D. Nuclear

Answer: C Explanation: Combustion is a chemical process. It is another word for burning, and is not a form of energy.

What is conserved during a chemical reaction? A. Matter B. Neither matter nor energy C. Both matter and energy D. Energy

Answer: C Explanation: In any chemical reaction, both mass and energy are always kept the same, or preserved,

What kind of energy is stored within a chemical substance? A. kinetic energy B. free energy C. potential energy D. activation energy

Answer: C Explanation: Potential energy is stored energy. Kinetic energy, which is related, is energy in motion. The other two kinds of energy have severely unrelated meanings. Potential energy is therefore the only choice that makes sense in this question.

Which process is exothermic? A. boiling of water B. melting of copper C. condensation of ethanol vapor D. sublimation of iodine

Answer: C Explanation: The only process where energy is being released is the condensation of ethanol vapor. Condensation is exothermic because it is the change of a substance from gas to liquid, which releases thermal energy.

The boiling point of water at standard pressure is A. 0.000 k B. 100.K C. 273 K D. 373 K

Answer: D Explanation: As seen in the Chemistry reference table, the boiling point of water is 100 degrees Celsius. To convert that to Kelvin, add 273, and you get 373 K.

Which unit is used to express the energy absorbed or released during a chemical reaction? A. torr B. kelvin C. volt D. joule

Answer: D Explanation: Joules are the only unit used in thermochemistry. Kelvin is a unit for temperature, and the other two units are completely unrelated.

Another name for heat energy is A. activation energy B. endothermic energy C. exothermic energy D. thermal energy

Answer: D Explanation: Thermal energy, simply stated is heat energy.

What occurs when a substance melts? A. It changes from solid to liquid, and heat is released. B. It changes from liquid to solid, and heat is released. C. It changes from liquid to solid, and heat is absorbed. D. It changes from solid to liquid, and heat is absorbed.

Answer: D Explanation: When a substance melts, it is changing from the solid-state to the liquid state. This implies that is changing from a solid to a liquid. This kind of change absorbs energy because, in order for a substance to melt, it needs to gain enough thermal energy to do so. Therefore, the answer is D.

Under what circumstances would you be required to find the Heat of Vaporization of a substance?

Answer: If there is no temperature range given. Explanation: If there is no range of temperature provided, you will be most likely required to find the value of heat of vaporization, and multiple that by the mass given.

Why would Br2 be a liquid and I squared be solid at STP? Answer in terms of intermolecular forces.

Answer: Molecules of I squared , or Iodine, have stronger intermolecular forces. Explanation: Intermolecular forces can determine the phase of a substance. A lower one can mean a substance may be a liquid, while a higher one may cause a substance to be a solid.

In the equation, q=mCAT, what does the AT (delta T) represent?

Answer: Temperature change Explanation: As seen in the reference table, on Table T, the value of delta T is equivalent to the change in temperature.

In a closed system, what equals the amount of heat gained?

Answer: The amount of heat lost. Explanation: In a closed system, heat gained = heat lost. This is due to the Conservation of Energy.

What is a calorimeter used for?

Answer: To measure potential energy. Explanation: One way to measure the potential energy of a substance is with a calorimeter.

What would the temperature of a flask also indicate?

Answer: he average kinetic energy of the flask Explanation: The average kinetic energy of the flask is the same as its temperature.