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CHM 2040 Lecture Notes - Lecture 5: Contin, Exothermic Process, Junkers J 1

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25 Dec 2014

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Chemical hand warmers: most hand warmers work by using the heat released from the slow oxidation of iron. 4 fe(s) + 3 o2(g) 2 fe2o3(s) Nature of energy: the amount your hand temperature rises depends on several factors: Mainly, the amount of heat released by the reaction: even though chemistry is the study of matter, energy affects matter, energy is anything that has the capacity to do work, work is a force acting over a distance. Energy = work = force distance: heat is the flow of energy caused by a difference in temperature, energy can be exchanged between objects through contact. Classification of energy: kinetic energy is energy of motion or energy that is being transferred, thermal energy is the energy associated with temperature. Thermal energy is a form of kinetic energy: potential energy is energy that is stored in an object, or energy associated with the composition and position of the object.

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Related Questions

Energy cannot be created nor destroyed, but it can be transferred between a reaction and its surroundings. The change in energy, Delta E, is positive if the reaction absorbs energy, and it is negative if the reaction releases energy. You may also see this expressed in terms of change in internal energy, Delta U. For the purposes of this question, Delta U and Delta E are equal. One way a reaction can transfer energy to or from the surroundings is by releasing or absorbing heat. A reaction can also transfer energy, in the form of work, through a change in volume. The total change in energy is the sum of the heat and work: Delta E = q + w At constant pressure, q = Delta H and w = -P Delta V and so Delta E = Delta H - P Delta V Assuming constant pressure, rank these reactions from most energy released by the system to most energy absorbed by the system, based on the following descriptions: Surroundings get colder and the system decreases in volume. Surroundings get hotter and the system expands in volume. Surroundings get hotter and the system decreases in volume. Surroundings get hotter and the system does not change in volume. Also assume that the magnitude of the volume and temperature changes are similar among the reactions. Rank from most energy released to most energy absorbed. To rank items as equivalent, overlap them. Energy cannot be created nor destroyed, but it can be transferred between a reaction and its surroundings. The change in energy, Delta E, is positive if the reaction absorbs energy, and it is negative if the reaction releases energy. You may also see this expressed in terms of change in internal energy, Delta U. For the purposes of this question, Delta U and Delta E are equal. One way a reaction can transfer energy to or from the surroundings is by releasing or absorbing heat. A reaction can also transfer energy, in the form of work, through a change in volume. The total change in energy is the sum of the heat and work: Delta E = q + w At constant pressure, q = Delta H and w = -P Delta V and so Delta E = Delta H - P Delta V A mole of X reacts at a constant pressure of 43.0 atm via the reaction X(g) + 4Y(g) - 2Z(g), Delta H degree = -75.0 kJ Before the reaction, the volume of the gaseous mixture was 5.00 L. After the reaction, the volume was 2.00 L Calculate the value of the total energy change. AE, in kilojoules. Express your answer with the appropriate units.

Experiment 11 ENTHALPY OF REACTION (HESS'S LAW) IDEAS Both the physical and biological worlds are characterized by a complex interplay of chemical reactions. In all chemical reactions, heat is released or absorbed. Combustion is one of the commonly observed chemical reactions accompanied by the evolution of heat energy, which may be harnessed of for such as the heating of homes, or which may be converted to other forms energy, such as mechanical energy in the steam engine or the internal combustion engine. One of the pioneering studies on the heat of chemical reactions was made by Lavoisier and ace in 1 Investigating the heat associated with various reactions, including combustion, they showed that each reaction was associated with a specific amount of heat and that the heat evolved in chemical reaction is equal to the heat absorbed in the reverse reaction. Lavoisier had proposed the modern theory of combustion as the combination of a substance with aygen. He also suggested the hypothesis that respiration is merely slow combustion. With Laplace, Lavoisier attempted to compare the quantity of heat given off by a burning candle with that given off by a live chicken. The quantity of heat was determined by measuring the quantity of ice that melted, in an insulated container, in the presence of the candle or the chicken. Little progress was made in thermochemistry until about fifty years later, when G. Hess (1802- 18500 studied heats of reaction in greater detail and stated the law a840) that bears his name: The heat evolved or absorbed in a chemical reaction is the same whether the process is accomplished in one step or in many. The law suggested, therefore, that both the reaction and the thermodynamic data could be treated algebraically. Although it was an empirical law when Hess proposed it, it was theoretically justified a few years later when the principle of conservation of energy was proposed. Hess's law can be illustrated by the following problem. Calculate the change in heat (AH) for the following reaction: 1. Mgo(s) 2H+(aq) Use the following information to solve the problem: AH- -35 kl/mole AH -56 kJ/mole 3, H+(aq) oHraq)