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CHEM1100 Lecture Notes - Lecture 15: Exothermic Reaction, Energy, Thermodynamics

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25 May 2018

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Lecture 15 - Thermodynamics!

Thermodynamics

Energy can be harnessed to provide heat and work !

It is the quantitative study of the transformation of energy !

Combustion reaction !

Anything + oxygen = carbon-dioxide + water !

Energy transfer

•Work and Heat are the two fundamental ways in which energy is transferred to or from a

system.!

•System = the chemical reactants and products. The system is our frame of reference and what

we can experimentally measure. Always think from the point of the system. !

•Energy is transferred into or out of a system by or into the surroundings. !

System !

The system is allowed to interact with the surroundings. !

The system is closed oﬀ from the surroundings so no matter can enter.

But system is inﬂuenced by energy (heat etc)!

The system cannot be inﬂuenced by anything. Eg: the universe is an

isolated system. !

Adiabatic systems: can only exchange energy in the form of work with the surroundings !

First law of thermodynamics

Energy is neither created nor destroyed, just transferred from one form to another.

•energy is transferred in the form of heat (q) and work (w)!

∆U = q + w

U = the energy !

Q = heat added to the system. !

• If q < 0 it is exothermic!

W = work done on the system. !

Change in internal energy

= the heat added to the

system + the extra work

done on the system.

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Document Summary

Energy can be harnessed to provide heat and work. It is the quantitative study of the transformation of energy. Energy transfer: work and heat are the two fundamental ways in which energy is transferred to or from a system, system = the chemical reactants and products. The system is our frame of reference and what we can experimentally measure. Always think from the point of the system: energy is transferred into or out of a system by or into the surroundings. The system is allowed to interact with the surroundings. The system is closed o from the surroundings so no matter can enter. But system is in uenced by energy (heat etc) Adiabatic systems: can only exchange energy in the form of work with the surroundings. Energy is neither created nor destroyed, just transferred from one form to another: energy is transferred in the form of heat (q) and work (w)

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Related Questions

1.) Which statement isincorrect?

(a) Energy is the capacity todo work or to transfer heat.

(b) Kinetic energy is theenergy of motion.

(c) Potential energy is the energy that a system possesses by virtue ofits position or composition.

(d) A process that absorbsenergy from its surroundings is called exothermic.

(e) The Law of Conservation of Energy is another statement of the FirstLaw of Thermodynamics.

2. Which of the following statementsabout the first law of thermodynamics and energy is false?

(a)Kinetic energy cannot be convertedto potential energy.

(b)Kinetic energy =1/2mv².

(c)All the energy in the universe isconserved.

(d)A system can never decrease itsenergy.

(e)Potential energy is the energy ofposition or composition.

3. Whichone of the following thermodynamic quantities isnot a state function?

(a)work (b) enthalpy (c)entropy (d) internalenergy (e) free energy

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.