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Energetics and Thermodynamics

Thermodynamics is a branch of Energetics concerned with the concepts of heat, energy and work. It focuses on variables which apply at the macroscopic levels, such as temperature, enthalpy (deltaH) and entropy (deltaS); and analyzes their behavior based on the nature of the microscopic constituents. The examination of these variables may include the study of how they are related to each other, by what specific thermodynamic laws, and how each variable changes over time. Thermodynamics applies to a range of subjects such as physics, engineering and astronomy. In chemistry, thermodynamics applies mainly to the energy of chemical reactions, phase changes and reaction mechanisms. For example, if a given chemical reaction releases energy, then thermodynamically speaking, it is known as an exothermic reaction. If the overall reaction absorbs energy, then it is known as an endothermic reaction. Whether there are any phase changes depends on the reactants and the nature of their interactions to form the products. For example, the combustion of methane is an exothermic reaction with a phase change: CH_4(g) + 2O_2(g) --> CO_2(g) + 2H_2_O(l) deltaH = -891.1 kJ*mol^(-1) In the above reaction, since delta H is negative, the reaction is exothermic. Also, it can be seen that both reactants are in the gas phase, while the products consist of a gas and a liquid, suggesting that a phase change has occurred during the course of the chemical reaction. Thus, studying the thermodynamics and energetics of a system can help predict the direction and outcome of a chemical reaction – whether a reaction is favorable or not given the physical conditions, and if it is favorable, how do the reactants interact and how energy is involved.

Categories within Energetics and Thermodynamics

Phase, State and Energy Changes

Postings: 4

Phase and State Changes refer to the transformation of a thermodynamic system from one phase or state to another.

Reaction Intermediates and Mechanisms

Postings: 62

In a Reaction Mechanism, a Reaction Intermediate is a molecular entity that is formed by the reactants which reacts further to form the products.

Hess’ Law

Postings: 9

Hess’s Law states that the total enthalpy change accompanying a particular chemical reaction is independent of the pathway between the initial and final states.

Raoult's Law

Postings: 2

Raoult’s Law states that the vapor pressure of an ideal solution is dependent on the vapor pressure and mole fraction of each chemical component in the solution.

Law of Conservation of Mass

Postings: 1

The Law of Conservation of Mass states that for any system closed to all transfers of mass and energy, the mass of the system must remain constant over time.

Vapor Pressure of Mixtures of Miscible vs. Immiscible Liquids

Consider a physical explanation for the difference of vapour pressure of miscible and immiscible solutions. For immiscible the total vapour pressure is equal to the sum of the pressure from the pure liquids but and miscible liquids pressure vapour pressure follows raoults law. What is the physical justification for this?

Mathematically defining that a process is reversible

I have a question about relations for a process even though I am unsure about the scope of this. Still I wonder about a mathematical relation for the following: I wonder about how one defines mathematically that a process is reversible for a process that has both pressure and temperature differences from definition of total e

Specific Heat & Enthalpy

Question #1 A 25.000g sample of unknown metal is heated to 99.5 degrees Celsius and added to 50.0mL of water in a calorimeter, which has an initial temperature of 22.o degrees Celsius (density of water is 0.99780 g/mL. The temperature of the calorimeter increases to a maximum temperature of 33.5 degrees Celsius. The heat capa

A Discussion On Delta S Values

Using the data sheet (see attachment) calculate delta S values for the following reactions. In each case explain the sign of delta S. N2H4(g) + H2(g) --> 2NH3(g) 2Al(s) + 3Cl2(g) --> 2AlCl3(g) Mg[OH]2(s) + 2Hcl(g) --> MgCl2(s) + 2H20(l) 2CH4(g) --> C2H6 + H2(g)

Gas Laws & Heat Of Reaction

1. For the reaction 2 NO(g) + O2(g) -->2 NO2(g) deltaH = -126.0 kJ at 25C. (a) Calculate the amount of heat transferred when 333 g of NO(g) reacts with O2(g) at 25C and 1 atm. (b) Does this heat flow into the system or does it flow to the surroundings? (c) Is this reaction exothermic or endothermic? 2. If 8675 J of

Van der Waals Gas Equation

The equation of state of one mole of a van der Waals gas is given by (P+a/(v^2))(V-b) = RT with a and b are constants. a) Calculate the work W in an isothermal reversible process when volume changes from V1 to V2. b) Using the energy equation, show that (du/dV) = a/v^2 c) Calculate the change in internal energy U in th

Molar Mass of Butane

1-HgO(s) Hg(l) + O2(g) Consider the unbalanced equation above. A sample of impure mercury(II) oxide is heated and the HgO decomposed completely. If 680. mL of O2 is collected by displacement of water at a barometric pressure of 680.0 mm Hg and 25.0°C, what mass of HgO was originally present? The vapor pressure of water is 23.

Enthalpy and ratio of slopes and graph

1. Consider the phase change: C(graphite) <---> C(diamond) Given that delta_rG^o/Jmol^-1 = 1895 + 3.363T, calculate the enthalpy and entropy. Calculate the pressure at which diamond and graphite are in equilibrium with each other at 25 degree Celsius. Take the density of diamond and graphite to be 3.51 g/cm^3 and 2.25 g/c

Thermal Interactions and Enthalpy

Thermal Interactions Part 1: In an insulated container, you mix 200. g of water at 80ºC with 100. g of water at 20ºC. After mixing, the temperature of the water is 60ºC. a. How much did the temperature of the hot water change? How much did the temperature of the cold water change? Compare the magnitudes (positive values) o

Heating a pot of water with pentane

You are out camping with your family and you decide that you would heat some water for cooking your food. The pot you use is made from aluminum (heat capacity, s, = 0.902 J/g@EC). The pot has a mass of 675.6 g and a capacity of 1.356 L. You are going to heat water (s = 4.184 J/g degrees C) starting from ice (s = 36.93 J/mol degr

Numerical Problems related to Vaporization & Thermodyamics

At 100 degrees Celsius and 1.00 bar, 1.00 mol of liquid water is converted to 1.00 mol of gas. a) Calculate delta Hm, delta Sm and delta Gm. (Look up the standard enthalpy of vaporization at the normal boiling point. Give your source). b) 1.00 mol of liquid water is placed in a previously evacuated chamber at 100 degrees Cel

Enthalpy of Formation Problems

Please help with the following problem. Many power plants produce energy by burning carbon-based fuels, which also produces carbon dioxide. Carbon dioxide is a greenhouse gas, so over-production can have negative effects on the environment. Use enthalpy of formation data to calculate the number of moles of CO_2 (g) produce

Calorimeter experiment

Calorimeter experiment: Refer to attachments for full experimental design. I need help with the following questions: 1. Why is it necessary to start this experiment with a large excess of ice in the metal ice container (the calorimeter)? 2. If all the ice melts when you were doing this experiment so at the end of the

Three common hydrocarbons that contain four carbons

103. Three common hydrocarbons that contain four carbons are listed here, along with their standard enthalpies of formation 1,3 Butadiene, C4H6(g), 111.9 Kj/mol 1-Butene, C4H8 (g), 1.2 Kj/mol n-butene, C4H10(g) -124.7Kj/mol heat formation a) For each o these substances calculate the molar enthalpy of combustion to CO

Thermodynamics: Mass and Temperature

Please help answer the following question. What mass of water at 100 degrees Celsius would raise the temperature of 30.00g of water at 23.0 degrees C to 32.6 degrees C? For this question, assume that the calorimeter does not absorb any heat. (please show the work)

Balanced thermochemical equations and Reaction Heat

The complete combustion of acetic acid, HC2H3O2(l) to form H2O(l) and CO2(g) at a constant pressure releases 871.7kJ of heat per mole of HC2H3O2. a) Write a balanced thermochemical equation for this reaction. The answer is HC2H3O2(l) + O2(g)---->2 H2O(l) + 2 CO2 Change (^) H = -871.7kJ b) My question is, if I onl

Thermodynamics: Enthalpy of reaction

Please help answer the following thermodynamics questions. a) When a 3.88g sample of solid ammonium nitrate dissolves in 60g of water in a coffee-cup calorimeter, the temperature drops from 23 degrees C to 18.4 degrees C. Calculate ^H (in kJ/mol NH4NO3) for the solution process NH4NO3(s)---->NH4(aq) + + NO3 - Assu

Chemistry: Limiting Reagent and Enthalpy Sample Questions

I am having trouble setting up the follow problems. I am not even sure where to start. If anyone can offer any advice, I would greatly appreciate it, as I am completely stumped: 1) The volume in Liters of H2(g), measured at 22 degrees C and 745 mmHg, required to react with 30.0 L of CO (g), measured at 0 degrees C and 760 mmH

formula and calculation

State all of the assumptions (e.g. ideal gas etc). (a) Starting with dGm = VmdP-SmdT, derive the relationship (Clayperon Equation) that expresses the slopes between the solid/liquid/gas phase boundaries in a Pressure versus Temperature plot. (b) Using the Clayperon equation from part a, justify the difference in the solid-li

Skeletal Reactions for Combustion

State all assumptions (e.g. ideal gas etc). Given the followin skeletal reaction for the combustion of hydrogen to generate water using the tables attached to the test: 2H??2(g) + O2(g) ----> 2H2O(g) (a) Determine the Î"HO, Î"So, and Î"Go for the above reaction at 298 Kelvin at 1 bar pressure. (b) Justify and compare

Free Energy and thermodynamics

Please help answer the following questions. See the attached file for multiple choice options. 1. Which sample of sulfur at 25°C has the greatest entropy? 2. What is the standard free energy change for the following reaction at 25°C: C(diamond) ---> C(graphite) 3. Which sample of H2O has the least entropy? 4. Which su

Specific Heat

Could you please take a look at this? I'm having trouble with #2 and #3. Thank you! Observations: #1 - Initial temperature of Iron shot (Fe) metal: 100°C Final temperature of Iron shot (Fe) metal: 28°C Initial temperature of water from calorimeter: 20°C Final water temperature from calorimeter: 28°C #2

Heat Capacity, Enthalpy, Intermolecular Forces and Radius of Platinum Atom

1.Calculate the amount of heat that must be absorbed by 10.0 g of ice at -20 C to convert it to liquid water at 60.0 C. Given: Specific heat (ice)=2.1 J/goC Specific heat(water)=4.18 J/goC H (fus)=6.0 kJ/mol 420 J 2,900 J 6,300 J 63 kJ 7.5 J 2. The major enthalpy of Boron tribromide (BBr3) is 30.5 kJ/mol, and its norma

Calories and Diet

Please explain the relationship between calories, food, and heat by responding to the following prompts: 1. List the 'magic formula' for weight loss. List a high-calorie food and a low calorie food. Do you see a relationship between the high calorie foods and the low calorie foods (other than the number of calories?) I ca

Chemistry: Equilibrium Concentration Sample Questions

a) What is the expression for the eqilibrium constant K in terms of the concentrations of the products and reactants for the reaction between ammonia, (NH3 (aq)) (SMALL 3), WHICH REACTS WITH WATER TO PRODUCE AMMONIUM (NH4 + (aq)) and hydroxide (OH - (aq)) ions. NH3 (aq) + H20 (l) = NH4+ (aq) + OH- (aq) the enthalpy cha