Thermochemistry

 [|Page 302] [|Page 304] [|Page 305]


 * __5.1__ Changes in Matter and Energy**

//Practice, page 300.// b. Physical change, since the composition of the ice remains the same, and there is only a change of state. c. Chemical change, see a. d. Physical change, see b. e. Chemical change, since the composition of the reactants are changed. f. Physical change, see b.
 * 1.**a. Chemical change, since the composition of the gas changes, and the energy released is chemical potential energy from the bonds.

a. The burning gas (and oxygen, and the combustion products) comprise the system. The barbecue comprises the surroundings. b. The ice is the system, and the hand comprises the surroundings. c. See a. d. The wax is the system, and the stove is the surroundings. e. The zinc, acid solution, and products of the reaction comprise the system. The beaker is the surroundings. f. The ice is the system; its packaging and the injury it is on are the surroundings.
 * 2.** Note that in all of these, it is assumed that only what is mentioned in the question is present. Anything else would be a part of the surroundings.

a. Isolated during the explosion, since the neither the gases nor the heat produced can escape (assuming that the cylinder is an incredible insulator). b. Open, since water vapour can leave the system and heat can enter it. c. Open, as both heat and produced gases can escape the system. d. Open, as both heat and hydrogen gas can escape the system (unless it is sealed and insulated, in which case it is isolated). e. Open, since both heat and gases can escape the system.
 * 3.** Note that an isolated system is ideal, so all of these are actually open systems.


 * 4.** Thermal energy is the “energy available from a substance as a result of the motion of its molecules”, as defined on page 298 of the textbook. Since the pool has a much larger mass than a thimble, it has more molecules of water and so more thermal energy. The higher temperature of the water in the thimble only means that the average kinetic energy of its particles is higher, not necessarily the total kinetic energy.

b. Exothermic, since reaction also releases heat. c. Endothermic, since the metal absorbs heat to melt.
 * 5.**a. Quite exothermic, as the reaction releases a great deal of heat.

b. Since systems naturally tend towards minimum enthalpy, the most commonly encountered reactions are exothermic.
 * 6.**a.
 * //Change// || //Type of Change// || //Endo- or Exothermic// || //Type of System// ||
 * paper burning in safe || chemical || exothermic || isolated ||
 * melting glacier || physical || endothermic || open ||
 * dew forming on grass || physical || exothermic || open ||
 * baking bread || chemical || endothermic || open ||
 * fusion of hydrogen || nuclear || exothermic || open ||

a. This is explained in the first link. b. I assume this would have been explained in the second (now broken) link. The ‘burning’ refers to the use of stored energy in metabolic processes. c. This is explained in the third link.
 * 7.** The textbook resources are found [|here], sorted by page number.

 //**Page 302.**//
 * 8.** Since the aluminum sample has the lowest specific heat capacity, less energy is required to raise its temperature, compared to the other two samples. As such, it would undergo the greatest temperature change.





//Practice, page 304.//**
 * 


 * 14.** Delta H is an enthalpy change. It is the energy absorbed from or released to the surroundings when a system changes from reactants to products. It is the change in potential energy of the surroundings. q (surroundings) is the change in kinetic energy of the surroundings. They are similar because they are both consistent with the Law of Conservation of Energy. Energy may be converted or transferred during a reaction but the total energy of the system and its surrounding remains the same. H and q(surroundings) are equal to each other.


 * 15.** Enthalpy Changes for Physical, Chemical and Nuclear Changes:

v Temperature changes during dissolving of pure solutes ||
 * =Physical Changes= ||
 * v Energy is used to overcome or allow intermolecular forces to act ||
 * v Fundamental particles remain unchanged at the molecular level ||
 * v Temperature remains constant during changes of state
 * v Temperature remains constant during changes of state
 * v Temperature remains constant during changes of state
 * v Typical enthalpy changes are in the range delta H = 10° – 10² kJ/mol ||
 * =Chemical Changes= ||
 * v Energy changes overcome the electronic structure and chemical bonds within the particles (atoms or ions) ||
 * v New substances with new chemical bonding are formed ||
 * v Typical enthalpy changes are in the range delta H = 10² – 10^4 kJ/mol ||
 * =Nuclear Changes= ||
 * v Energy changes overcome the forces between protons and neutrons in nuclei ||
 * v New atoms, with different numbers of protons and neutrons are formed ||
 * v Typical enthalpy changes are in the range delta H =10^10 – 10^12 kJ/mol. The magnitude of the energy change is a consequence of Einstein’s equation Emc² ||
 * =Nuclear Changes= ||
 * v Energy changes overcome the forces between protons and neutrons in nuclei ||
 * v New atoms, with different numbers of protons and neutrons are formed ||
 * v Typical enthalpy changes are in the range delta H =10^10 – 10^12 kJ/mol. The magnitude of the energy change is a consequence of Einstein’s equation Emc² ||
 * v New atoms, with different numbers of protons and neutrons are formed ||
 * v Typical enthalpy changes are in the range delta H =10^10 – 10^12 kJ/mol. The magnitude of the energy change is a consequence of Einstein’s equation Emc² ||
 * v Typical enthalpy changes are in the range delta H =10^10 – 10^12 kJ/mol. The magnitude of the energy change is a consequence of Einstein’s equation Emc² ||



//**Understanding Concepts, page 305.**//

liquid --> gas is endothermic liquid -->solid is endothermic solid --> liquid is endothermic solid --> gas is endothermic gas --> solid is endothermic gas --> liquid is endothermic
 * 1**. For the six possible changes of states of the three states of matter, they are:


 * 2.** The three factors involved in the calculations of the amount of heat absorbed or released in a chemical reaction are; the mass (m), the temperature change ( delta T ), and the type of substance (the specific heat capacity).

(b) water evaporating from a lake is a **physical change** because there are no changes to the molecular structure and it is simply changing state. (c) uranium fuel encased in concrete in a reactor is a **nuclear change** because the uranium is decaying to form new atoms
 * 3.** (a) gasoline burning in a car engine is a **chemical change** because energy is released in the form of chemical potential energy and the molecular composition changes.

(a) the chemical system is an open system and the surroundings include the air surrounding the car, the road, and the car itself. (b) the chemical system is an open system and the surrounding includes the air over the lake and the water in the lake. (c) the chemical system is a closed system, and the surroundings are the concrete and whatever else may be encasing the uranium.
 * 4.** – is referring to the situations from question 3 a, b and c.

(a) is an open system because the gasoline burning is a combustion reaction relying on a constant supply of oxygen from the atmosphere. (b) is an open system as the evaporated water is released into the atmosphere. (c) is an isolated system as it is contained within concrete in a reactor and no outside influences are acting on the decay.
 * 5. -** is referring to the situations from question 3 a, b and c.

(a) the chemical system is an open system because energy can flow into and out of the system. Relatively 10° – 10² kJ/mol would be transferred in this system. (b) the chemical system is an open system because energy can flow into and out of the system. Relatively 10² – 10 kJ/mol would be transferred in the system. (c) the chemical system is a closed system consisting of whatever is encased within the concrete of the reactor. Relatively 10 – 10 kJ/mol would be transferring in this system.
 * 6.** – is referring to the situations from questions 3 a, b and c.

7. Information on bomb calorimeter can be found [|here] under Section 5.1 Questions page 305.

8. Information on hot and cold packs that use chemical reactions can be found [|here] under Section 5.1 Questions page 305.



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