CHEM 001 Lecture Notes - Lecture 23: Enthalpy, State Function, Exothermic Process

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skywildebeest596

13 Aug 2020

School

College of The Sequoias

Department

Chemistry (CHEM)

Course

CHEM 001

Professor

Rodriguez

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Document Summary

Because this is a state function, the path to get here doesn"t matter. C. endothermic: enthalpy change is positive; heat flow to the system (in a constant pressure reaction) D. exothermic: enthalpy change is negative; heat flow to the surroundings (in a constant pressure reaction) The energy released comes from the intermolecular potential energy of the bonds, not the kinetic energy. A. hess"s law: sum of the enthalpy changes for each step is equal to the total enthalpy change regardless of the path chosen. Forward reaction has the exact opposite change in enthalpy as the reverse. A. activation energy: minimum kinetic energy threshold to collide molecules and make babies. Transition state: the highest energy point in a reaction where old bonds are breaking and new bonds are forming; not the same as intermediates. C. intermediates: products of one step that are the reactants for the next step.

Related Questions

*This is a Chemical Engineering question, that just inst a category choice**

A 831.0 g/hr stream of liquid methyl alcohol, also called methanol, (CH3OH) at 5.80 atm and 18.0Â°C was held at constant pressure, vaporized and brought to 236.0Â°C. Assume that methyl alcohol vapor behaves ideally for the temperature range and pressure given. FIND: The rate heat must be supplied to this system, Because this is an open system and there is no change in kinetic energy, potential energy, or shaft work, the rate of heat supplied to the system is equal to the rate of change in enthalpy of the process.

The change in enthalpy is a state property, meaning that it is path independent. Since table values for the specific enthalpy of methyl alcohol at the starting and final conditions are not available, you will have to calculate the change in enthalpy as the sum of a series of steps. Because the methyl alcohol is going from a liquid to a vapor, you know that you will need to utilize the heat of vaporization at some temperature, and the heat capacity equations of the liquid, the vapor, or both. You will also need the molar mass of methyl alcohol and its specific gravity. Choose the path that will allow you to calculate the total enthalpy change given these physical constants. Calculate the sum of each step\'s specific enthalpy, and multiply this value by the molar flow rate of methyl alcohol into the process.

STRATEGY: 1. Look up the relevant physical constants of methanol. 2. Determine the proper path to take. 3. Find ?H1. 4. Find ?H2. 5. Find ?H3. 6. Find ?Htot. 7. Find ?H. 8. Find Q.

Imagine a container placed in a tub of water, as depicted in the accompanying diagram. (a) If the contents of the container are the system and heat is able to flow through the container walls, what qualitative changes will occur in the temperatures of the system and in its surroundings? What is the sign of q associated with each change? From the system’s perspective, is the process exothermic or endothermic? (b) If neither the volume nor the pressure of the system changes during the process, how is the change in internal energy related to the change in enthalpy?

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Show your work for all calculations.

1. When 1.104 grams of iron metal are mixed with 26.023 grams of hydrochloric acid in a coffee cup calorimeter, the temperature rises from 25.2 Â°C to a maximum of 33.5 Â°C. The reaction that occurs is given below.

2Fe(s)+6HCl(aq) â 2FeCl3 (aq)+3H2 (g)

a) Determine the amount of heat (in J) absorbed by the reaction mixture. Assume that the specific heat capacity of the mixture is the same as the specific heat capacity of water.

b) How much heat (in J) was released by the reaction that occurred?

c) Is this reaction exothermic or endothermic? Is ÎHreaction positive or negative?

d) Under constant pressure conditions (as used in this experiment), the heat released by the reaction equals the reaction enthalpy, qreleased = ÎHreaction. Determine ÎHreaction in Joules per gram of metal used (J/g).

e) Determine ÎHreaction in kilojoules per mole of metal used (kJ/mol).

f) Determine ÎHreaction in kilojoules per mole for the balanced reaction equation provided (kJ/mol). ï¿¼ï¿¼ï¿¼ï¿¼ï¿¼ï¿¼ï¿¼

2. Consider the following three reactions:

2Fe(s)+6HCl(aq) â 2FeCl3 (aq)+3H2 (g) ÎHA

Fe2O3 (s)+6HCl(aq) â 2FeCl3 (aq)+3H2O(l) ÎHB

2H2 (g) + O2 (g) â 2H2O(l) ÎHC

Show how these equations must be summed together according to Hessâs Law to determine ÎH for the combustion of iron (target equation shown below). Also show clearly how the ÎH values of each of the three reactions must be manipulated to determine the enthalpy of combustion of iron.

4Fe(s)+3O2 (g) â 2Fe2O3 (s) ÎH=?

3. Using tabulated ÎHfÂ° values in the text, determine the enthalpy change (in kJ/mol) that occurs during the formation of water from its elements as described by the equation:

2H2 (g) + O2 (g) â 2H2O(l) ÎH=?

CHEM 001 Lecture Notes - Lecture 23: Enthalpy, State Function, Exothermic Process

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