Answer: 2

Why? The kinetic energy of a particle is the energy of motion of the particle relative to a point of reference. For example, a bullet fired from a gun would have a high kinetic energy due to its motion relative to the target. However, a stationary bullet would have no kinetic energy, as it would not be in motion. If we use the example of a container of ethanol, then the kinetic energy of a volume of ethanol is dependent on how fast the ethanol particles were moving. The basic equation governing kinetic energy is:

E_k = (½) mv² where:

E_k = kinetic energy,

m = mass and

v = velocity.

With this in mind it becomes immediately apparent that kinetic energy is determined by mass and velocity. The velocity of a particle will change with increasing temperature. The resulting increase in energy from an increase in temperature would cause the particles to gain more energy to put into motion. As particles in the ethanol are always in random motion, when heat energy is applied the molecules gain more energy and begin to break the week Van Der Waals forces of attraction present in all liquids. This also results in an increase in the velocity of the particles regardless of the volume. Therefore, temperature is the most significant aspect influencing the kinetic energy of the ethanol and not the volume of ethanol. A decrease in volume would increase the number of molecular collisions, but only as a result of a decrease in the free space available for movement, and not an increase in energy.

Answering the Question:

Answer: (4)

Why? A chemical reaction is the combining of two or more particles (reactants) to form a new product. There are two things that are absolutely necessary for any chemical reaction to proceed:

1)      The reactants must collide with the correct orientation, and

2)      The reactants must possess sufficient energy to allow the reaction to spontaneously occur and continue (activation energy).

These two are required regardless of the elements involved. If the particles do not collide, then there is no chance of a reaction. The probability of two particles of correct orientation colliding is actually very low. This is one of the reasons why an increase in concentration of reactants increases the rate at which the reaction can occur.

Answering the Question:

Answer: (4)

Why? Potential energy is the stored energy of a body that can be used later to do work. In the case of a weight being lifted over your head, that weight has the potential to fall or do work in the form of falling. However, until it is released, it would not as yet have done work. The energy contained in the reactants of a chemical reaction and the energy contained in the product is the potential energy. For chemical reactions the difference in potential energy of the reactants and the potential energy of the products is important in order to determine if the reaction will require energy or release energy as it proceeds.

A chemical reaction is normally based on the movement of electrons. The forces of attraction of the nucleus towards the electrons must be overcome before an element will become involved in a chemical reaction. The energy required for the reaction to proceed and is called the activation energy, it is the energy that all chemical reactions require to proceed and must be overcome in order for the reaction to begin.

Kinetic energy is the energy being used for actual work and is defined as, the energy of an object, which has a mass m, due to its motion. The entropy of a system is that energy that is not used for useful work. It is what usually determines the efficiency of a process and can be used as a measure of the tendency of a chemical reaction to proceed spontaneously.

The heat of fusion, also known as the enthalpy of fusion, is the energy used in changing the state, from solid to liquid for example. The heat of reaction or the enthalpy of reaction is the energy involved in a chemical reaction going from reactant to product or vice versa. The heat of reaction is what determines whether a reaction is exothermic (gives off heat) or is endothermic (absorbs heat).

Answering the Question:

To answer the question it is important to understand the different forms of energy involved in a chemical reaction. However, it is very important to not confuse entropy and enthalpy. Heat required or produced during the course of a reaction or the energy of the system involves enthalpy, while entropy is more a measure of the tendency of the reaction to be driven in a particular direction. A good start to answering the question is to draw the potential energy diagram of a chemical reaction. The potential energy diagram below shows the reaction of hydrogen (H₂) and oxygen (O₂) to form water.

Diagram 3. showing a potential energy diagram of a chemical reaction

Answer: 2

Why? An operating electrolytic cell is used to separate or break down chemical compounds through a process known as electrolysis (using electricity to separate). This process is very important in manufacturing, especially for the separation of elements from the mined ores. This process requires high amounts of energy as it is used to drive a process that otherwise would not occur spontaneously. The electrolytic cell is composed of three components, the electrolyte, an anode and a cathode. The anode and cathode together are called electrodes. Anions will move towards the anode, while cations will move towards the cathode. The process involves the reduction and oxidation (redox for short) of the anode, cathode and electrolyte to proceed. A redox reaction involves the movement of electrons. When an atom is oxidized it has a loss of electrons or an increase in oxidation state. When an atom is reduced there is a gain of electrons or a decrease in oxidation state).

An electrolytic cell should not be confused with a Galvanic cell. An electrolytic cell uses electricity to drive a chemical reaction, while a Galvanic cell uses a chemical reaction to produce electricity.

The above diagram is a diagram of an electrolytic cell. It uses a cathode, an anode and an electrolyte (Na⁺Cl^-) to produce chlorine and hydrogen. The cell is connected to a power source, which is used to drive the reaction.

Answering the Question:

Answer (1) as incorrect, as was mentioned before Galvanic cells produce electrical energy, while electrolytic cells consume it, eliminating answer (1) as a possible answer. Answer three (3) says it uses radioactive nuclides. A nuclide is the name given to the combination of the protons and neutrons that make up the nucleus of an atom. When the nuclide has a greater number of neutrons than protons, it becomes unstable and in some cases radioactive. This is a not a necessary component of an electrolytic cell, also eliminating answer (3). Answer four (4) states that an operating electrolytic cell undergoes spontaneous redox reaction. The cell itself utilizes redox reactions at the anode and cathode to drive the process, however, the reaction is not spontaneous as it requires electrical energy to drive the process.

Answer: (3)

Why? Answering this question requires some familiarity with the process of combustion, electrolysis, nuclear fission and oxidation. Combustion is the burning of a fuel in the presence of oxygen. The reaction is an exothermic reaction, which means heat and, often, light result from combustion reactions. A combustion equation is a theoretical equation however, as many byproducts are produced when the equation moves towards equilibrium.

C₅H₁₂ + 8O₂ → 5CO₂ + 6H₂O + Energy

The process of electrolysis of water involves the consuming of energy, rather than the production of energy. Electrolysis involves the use of an electrical current being conducted from one electrode to another using water as the circuit. If sufficient electrical energy is provided then hydrogen and oxygen will be produced.

2H₂O + Energy → 2H₂ + O₂

Electrolysis is used to split the covalent bonds of water to produce hydrogen gas and oxygen.

Nuclear fission is the splitting of the nucleus of heavy atoms such as Uranium 235 into smaller atoms. Fission is an exothermic process, which means heat is produced as a result. The process of nuclear fission has been exploited for the generation of power in nuclear power plants. Nuclear fission used by power plants is a chain reaction process started by bombarding heavy elements such as Uranium 235 with high-energy neutrons.

²³⁵₉₂U + ¹₀n → ¹⁴²₅₆Ba + ⁹¹₃₆Kr + 3¹₀n + energy

Three neutrons are produced which will continue a chain reaction to produce 9 additional neutrons and so on.

The oxidation of iron, this process is one of the things responsible for the rusting of iron. The oxidation of iron is part of a category of reaction called redox reactions or reduction oxidation reactions.

Reduction of oxygen involves oxygen behaving as an electron acceptor:

O₂ + 4e^- + 2H₂O → 4OH^-

Oxidation of iron involved the donation of electrons:

Fe → Fe²⁺ + 2e^-

The oxidation of iron results in energy production in the form of electrons. However, an oxidation reaction is usually paired with a reduction reaction, which involves the utilization of electrons.

Together reduction and oxidation have been used to produce electricity.

Answering the Question:

This question can be answered without knowledge of exactly how much energy is produced by each reaction type, by the process of elimination. Analyzing each answer in turn, answer (1) involves the combustion of an alkane.

The process of combustion will produce energy, making answer (1) a possible correct answer.

Answer (2) would not be a possible answer as the process of electrolysis consumes energy rather than produce it.

Answer (3) involves the process of nuclear fission, the splitting of the nucleus of an atom into smaller parts. Since this process is an energy producing process, it too is a possible answer.

²³⁵₉₂U + ¹₀n → ¹⁴²₅₆Ba + ⁹¹₃₆Kr + 3¹₀n + energy

Answer (4) is based on the oxidation of iron that does involve the transfer of electrons and could be used for the generation of power when paired correctly with other reactions. The process by itself however is not an energy producing reaction.

Answer: (1)

Why? A potential energy diagram is a measure of the potential energy of reactants and products relative to each other. The potential energy of reactants and products will indicate whether energy has been consumed (endothermic) during the reaction or released as a result of the reaction (exothermic). The diagram also indicates the activation energy or the energy that must be overcome before a reaction will proceed, regardless of the reaction being endothermic or exothermic.

Answering the Question:

The question shows a potential energy diagram of the reactants A and D forming product G. It also indicates that the reaction if endothermic, as the energy state of the product is higher than that of the reactants. This indicates that not only was the activation energy needed, but also that energy was supplied to the system in order for the reaction to continue. It is, therefore, important to know which of the answers would result in a product that would have required energy to be formed.

Answer: (4)

Why? Chemical reactions in equilibrium will always adjust to try and maintain that equilibrium. The above reaction would be categorized thermodynamically as exothermic. This means the forward reaction is producing heat as once of its products. If the temperature of the system is decreased, it means that the product in the form of energy is being removed. The forward reaction will, therefore, increase to compensate for the loss of heat, hence trying to place the system in a state of equilibrium. The reverse is also true, if the temperature is increased, then the equilibrium will shift towards the production of more reactant.

Answering the Question:

To answer the question, knowledge of how equilibrium reactions behave is important. Answer (1) suggests that a decrease in temperature (energy) would result in an increase of the reactants. As energy can be treated as a product in this situation, it could be equated to saying that if product is removed then the reactants would increase, and that is not possible. Answer (2) suggests that one reactant would increase (N₂) while the other reactant would decrease (H₂), which also seems unlikely. Answer (3) suggests that 1 product and 1 reactant would decrease, this also does not support the concept of equilibrium. Answer (4) suggests a decrease in reactant and an increase in product. Answer (3) is in agreement with the concept of equilibrium and is, therefore, the correct answer.

Answer: (3)

Why? A voltaic cell or Galvanic cell (named after Luigi Galvani, who discovered it in 1780) is an electrical cell that produces electrical energy from chemical energy (reactions) and is considered the precursor to the modern battery. Within the voltaic cell are a number of chemical reactions resulting in the movement of electrons. The voltaic cell is composed two different metals connected via a salt bridge. Each metal is used to make a half-cell, where in one half electrons are released, and on the other half, electrons are accepted. In the voltaic cell, negatively charged species will move toward the anode and away from the cathode.

The voltaic half-cell is composed of a copper rod, in a solution of a copper salt, while the other half-cell is composed of a zinc rod in a zinc salt solution. Both half-cells would be connected using a sodium chloride salt bridge. The chemical process would involve the movement of electrons from the zinc metal rod into solution; this would cause the zinc metal to dissolve. Electrons would cross the sodium chloride salt bridge into the copper salt solution. This Cu²⁺ would then receive the electrons and form Cu metal on the copper rod. Therefore, the cathode side of the reaction (the copper side) is carrying out the reduction portion of the reaction as it is receiving electrons, while, the zinc side of the reaction or anode, is donating electrons.

Answering the Question:

Answer: 66.8KJ

Why? The energy required to completely melt a 1g of a substance is called the heat of fusion. When a phase change occurs in a substance, the temperature of that substance will not change until the change is complete. This means that determining the heat energy required for the phase change cannot be calculated using a temperature change. The heat of fusion for a substance is constant for that substance and as a result can be used to determine the amount of energy required to melt or freeze a substance. Water is a well studied substance and is known to require 334J of energy per gram of ice to melt, or that much energy removed per gram of water to convert it to ice.

Answering the Question:

q = mH_fus

q is the total amount of heat involved
Hfus is the symbol for the molar heat of fusion. This value is a constant for a given substance.

m is the mass of the substance being assessed

Therefore         q =  Δh_fus(water) x (200/18)

q = 334 x (200)

Answer: q = mC∆T where;

q = the total amount of heat involved

m = mass

C = specific heat capacity

∆T = change in temperature

Therefore, q = mass of water x specific heat capacity of water x the change in temperature

q = 200 x 4.18 x (65-0)

q = 54340J or 54.34 KJ