Textbook Question
The enthalpy change for the reaction of 50.0 mL of ethylene with 50.0 mL of H2 at 1.5 atm pressure (Problem 9.51) is
∆H = -0.31 kJ. What is the value of ∆E?
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Ch.9 - Thermochemistry: Chemical Energy
Chapter 9, Problem 65
A reactiont akes place at a constant pressure of 1.10 atm with an internal energy change (ΔE) of 71.5 kJ and a volume decrease of 13.6 L. What is the enthalpy change (ΔH) for the reaction? (1 L-atm = 101.325 J)
Verified step by step guidance1
Convert the volume change from liters to joules using the conversion factor 1 L-atm = 101.325 J. Calculate the work done (W) using the formula W = -PΔV, where P is the pressure and ΔV is the volume change.
Ensure that the pressure is in atm and the volume in liters before substituting into the formula. Remember that work done on the system is negative if the volume decreases.
Calculate the enthalpy change (ΔH) using the formula ΔH = ΔE + W, where ΔE is the change in internal energy and W is the work done on the system.
Substitute the values of ΔE and W into the enthalpy change formula. Make sure the units of ΔE and W are consistent (both in joules or kilojoules).
Simplify the expression to find the enthalpy change ΔH for the reaction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Internal Energy (ΔE)
Internal energy (ΔE) is the total energy contained within a system, encompassing both kinetic and potential energy of the particles. In chemical reactions, changes in internal energy can result from heat transfer and work done on or by the system. Understanding ΔE is crucial for calculating other thermodynamic properties, such as enthalpy.
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00:40
Internal Energy
Enthalpy Change (ΔH)
Enthalpy change (ΔH) is a measure of the heat content of a system at constant pressure. It reflects the energy absorbed or released during a reaction, accounting for both internal energy changes and the work done due to volume changes. The relationship between ΔH and ΔE is given by the equation ΔH = ΔE + PΔV, where P is pressure and ΔV is the change in volume.
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02:34Enthalpy of Formation
Work Done by the System
In thermodynamics, work done by the system during a reaction can be calculated using the formula W = -PΔV, where P is the pressure and ΔV is the change in volume. A decrease in volume (ΔV < 0) indicates that the system is doing work on the surroundings, which affects the overall energy balance of the reaction. This concept is essential for accurately determining the enthalpy change.
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02:06Entropy of the System
Related Practice
Textbook Question
Assume that a particular reaction evolves 244 kJ of heat and that 35 kJ of PV work is gained by the system. What are the values of ∆E and ∆H for the system? For the surroundings?
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Textbook Question
What is the enthalpy change (ΔH) for a reaction at a constant pressure of 1.00 atm fi the internal energy chagne (ΔE) is 44.0 kJ and the volume increase is 14.0 L? (1 L-atm = 101.325 J)
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Textbook Question
What is the difference between heat capacity and specific heat?
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Textbook Question
Does a measurement carried out in a bomb calorimeter give a value for ∆H or ∆E? Explain.
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Textbook Question
Sodium metal is sometimes used as a cooling agent in heat-exchange units because of its releatively high molar heat capacity fo 28.2 J/(mol·°C). What is the specific heat and molar heat capacity of sodium in J/g·°C?
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