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CHEM 001 Lecture Notes - Lecture 9: Calorimetry, Enthalpy, Chemical Equation

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26 Aug 2020

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College of The Sequoias

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Chemistry (CHEM)

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The reaction whose q is to be measured occurs in an internal steel chamber (called a bomb) surrounded by water. The chamber"s volume is constant, therefore no work is done. The bomb and reactants are the system, the water bath is the surroundings. E = q (at constant volume) q cal = - q rxn qcal = - ccal x t cal (cal = calorimeter) qrxn = - ccal x t cal. The enthalpy, h, of a system is defined as: H only represents heat exchange; e is heat and work. For many reactions h and e are similar. H reaction = h products - h reactants. If h is positive, the reaction is endothermic. If h is negative, the reaction is exothermic. Coffee cup calorimeters run at atmospheric pressure and give h for reactions in solution. Heat is transferred to or from the reactants (system) to the solution (surroundings) Qsoln = cs soln m soln t soln.

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Related Questions

Please solve the first and the third questions

Bomb calorimetry is used to test the heat of formation for a new substance with the molecular formula C10H8. (MM=128.17 g/mol)

Part A. A 1.020g pellet of benzoic acid is placed in a constant volume bomb calorimeter containing only an oxygen environment. The bomb is placed inside an insulated jacket that contains 998.3 grams of water. The pellet is then ignited resulting in complete combustion of the pellet. The water temperature increases by 5.13 degC. Benzoic cid has a combustion constant of -26,434 J/g and the specific heat of water is 4.184 J/gdegC. Use this information to answer the following..

1. How much energy is produced by the reaction (qrxn)? Give your answer in KJ.

2. How much energy is absorbed by the water jacket (qwater)? Give your answer in KJ.

3. How much energy is absorbed by the calorimeter (minus the water) (qcal)? Give your answer in Joules.

4. What is the heat capacity constant for the calorimeter? Give your answer in J/K.

I know that #3=-26,434J/g(1.020g)

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.