Endothermic and Exothermic Processes

Because E, P, and V are state functions, H is also a state function, which means that AH depends only on the dijference between //final //j it,ai- The enthalpy change of a reaction, also called the heat of reaction, A/Z xn always refers to 

Therefore, because //products can be either more or less than //.eactants, the sign of AH indicates whether heat is absorbed or released in the change. We determine the sign of AH by imagining the heat as a reactant or product. When methane burns in air, for example, we know that heat is produced, so we show it as a product (on the right)  

CHAPTER 6 Thermochemistry Energy Flow and Chemical Change 

An endothermic ( heat in ) process absorbs heat and results in an increase in the enthalpy of the system. When ice melts, for instance, heat flows into the ice from the surroundings, so we show the heat as a reactant (on the left)  

In general, the value of an enthalpy change refers to reactants and products at the same temperature. 

Walls that permit heating as a mode of transfer of energy are called diathermic (Fig. 1.3). A metal container is diathermic and so is our skin or any biological membrane. Walls that do not permit heating even though there is a difference in temperature are called adiabatic. The double walls of a vacuum flask are 

Endothermic reactions are much less common. The endothermic dissolution of ammonium nitrate in water is the basis of the instant cold packs that are included in some first-aid kits. They consist of a plastic envelope containing water dyed blue (for psychological reasons) and a small tube of ammonium nitrate, which is broken when the pack is to be used. 

As an example of these terms, consider a chemical reaction that is a net producer of gas, such as the combustion of urea, (NH2)2CO, to yield carbon dioxide, 

When a process results in the evolution of heat, it is said to be exothermic (exo- is a prefix meaning out of ) that is, energy flows out of the system. For example, in the combustion of a match, energy flows out of the system as heat. Processes that absorb energy from the surroundings are said to be endothermic. When the heat flow moves into a system, the process is endothermic. Boiling water to form steam is a common endothermic process. 

Define exothermic and endothermic using the term surroundings instead of system. 

O Explain why energy is a state function, and why heat and work are not. 

O Explain the difference between potential energy and kinetic energy. 

O Write a paragraph explaining what happens to the balls using the terms potential energy, kinetic energy, work, and heat. 

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Read the entire laboratory activity. Form a hypothesis about how to distinguish exothermic and endothermic processes. Record your hypothesis on page 123. 

Give examples of important exothermic and endothermic processes. 

With the help of this analysis exothermic and endothermic process are measured which occur in a material as a function of the tem-... 

The counter-cocurrent concept features a modular design it provides separate heat exchanger loops for heat recovery within the endothermic mixture and the combustion gas. Cocurrent flow of exothermic and endothermic process streams is principally favorable with respect to the controllability of heat release. 

The enthalpy of reaction, AH, is the other important thermodynamic parameter to consider. On its own, whether a reaction is exothermic or endothermic will not determine if a reaction is industrially feasible or not. Both exothermic and endothermic processes are known in industry, methanol carbonylation to acetic acid (Equation 3 AH —123 kJ/mol at 200°C), being an example of the former and the steam reforming of methane to synthesis gas, (Equation 4 AH + 227 kJ/mol at 800°C), being an example of the latter. 

A generic reaction equation for the reversible hydrogenation of a metal, illustrating the exothermic and endothermic processes. 

Figure 6.6 Enthalpy diagrams for exothermic and endothermic processes. A, Methane burns with a decrease in enthalpy because heat leaves the system. Therefore, Hf,nsi < Hinitiai, and the process is exothermic AH < 0. B, Ice melts with an increase in enthalpy because heat enters the system. Therefore, Hfinai > Hinisai. and the process is endothermic AH > 0.

Heating and cooling system mechanics install, maintain, and repair refrigeration and heating equipment in homes and in industry. They must understand how heat is exchanged by means of exothermic and endothermic processes. They must be able to read blueprints and use a wide range of tools, from pipe cutters to computerized diagnostic devices. 

The Nature of Energy Temperature and Heat Exothermic and Endothermic Processes Thermodynamics Measuring Energy Changes... 

In general, there are many factors influencing the relationship between the rates of the exothermic and endothermic processes, that affect the carry-over in the flash smelting of oxidized lead-bearing feeds. They range fixrm the composition and dispersivity of the feed and carbonaceous fuel to the particular methods of feed preparation and the smelting conditions. Therefore, it is rather challenging to match the rates of heat release and heat consumption in the... 

The thermal decomposition of polymers involves exothermic and endothermic processes. Comparisons of experimental results obtained in the presence and absence of oxygen revealed that a pure thermal decomposition was not usually accompanied by exothermic heat changes while, during thermal oxidative decompositions, intensive heat evolution was generally observed. 

Adsorption and desorption are, respectively, exothermic and endothermic processes. Consequently, all practical adsorptive gas separation processes such as pressure swing adsorption (PSA) and thermal swing adsorption (TSA) are non-... 

DSC measures the temperature and heat flow associated with the transitions in materials as a function of time and temperature. Such measurements provide quantitative and qualitative information about the physical and chemical changes that involve exothermic and endothermic processes. 

Figure 6.17 shows the result of such measurements originating from those of Figure 6.16 by subtracting the furnace temperature Tp from I m of the sample system. The curves representing exothermic and endothermic processes clearly differ to a marked extent from one another. The delay Afo in recording the transition results from the heat transfer process between the substance and the temperature sensor. The other distortion in time (the time intervals Afi, Af2, and Atj) depends on the nature and quality of the heat conduction path between the heater and the temperature sensor in other words, it is associated with the apparatus used. 

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