Explore BrainMass

Energetics and Thermodynamics

Determining Velocity of Photon

I need some help with the following question: A photon with a wavelength of 3.091 x 10-7 m strikes an atom of hydrogen. Determine the velocity (in meters/second) of an electron ejected from the excited state, n = 3.

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

Heat of Metal

In this virtual lab, you will use coffee cup calorimetry to determine the specific heat, c, of a metal. Imagine that, in lab, you record the mass of a piece of metal, m_metal, as m_metal = 45.00 g In the next step of the lab (as shown in the animation in the attached document) you heat uo the piece of metal.

Water and Final Temperature

Two 20.0-g ice cubes at -14.0 degrees C are placed into 255 g of water at 25.0 degrees C. Assuming no energy is transferred to or from the surroundings, calculate the final temperature of the water after all the ice melts. heat capacity of H_2O(s) = 37.7 J/(mol*K) heat capacity of H_2O(l) = 75.3 J/(mol*K) heat capacity of

Fuel Value and Final Temperature

The amount of energy released by burning a fuel source, measured in energy per mass, is called the fuel value. If all the energy obtained from burning 1.28 pounds of ethane (fuel value is 11.36 kcal/g) is used to heat 130.0 kg of water at an initial temperature of 20.8 degrees C, what is the final temperature? ANSWER: _______

Molar Heat Capacity

Question: When 1243 J of heat energy is added to 44.3g of hexane, C6H14, the temperature increases by 12.4 degrees Celsius. Calculate the molar heat capacity of C6H14. Answer: ____ J/(mol*Celsius) HINT: The units of molar heat capacity, J(mol*Celsius), imply the formula needed to calculate it. Cp = q_p/(n(del

Calculating the Standard Enthalpy of a Reaction

Using the standard enthalpies of formation, what is the standard enthalpy of the following reaction? CO(g)+ H2O(g)?CO2 (g)+ H2 (g) ________________________________________ HINT: You can to look up the enthalpies of formation for the reactants and products here: https://sites.google.com/site/chempendix/thermo

Calculating the Final Temperature of Water

If the heat from burning 6.800 g of C6H6, 2C6Hy(l) + 15O2 (g)?12CO2 (g) + 6H2O (l) +6542 kJ is added to 5691 g of water at 21 degrees Celsius, what is the final temperature of the water? Note: The specific heat of H2O(l) is 4.184 J/(degrees Celsius). Also, use these conversion factors to find the amount of heat produced fr

Energy, Heat and Oxidation

The oxidation of copper(l) oxide, Cu_2O(s), to copper (ll) oxide, CuO(s), is an exothermic process, 2Cu_2 O(s) + O_s(s)=> 4CuO(s) deltaH_rxn^degrees = -292.0 kJ/mol Calculate the energy released as heat when 16.21 g of Cu_2O(s) undergo oxidation at constant pressure. ANSWER: __________ kJ HINT: When 2 mol Cu_2O(s) are

Evaluating the work(w) of a system

At constant pressure, which of these systems do work on the surroundings? 1. 2A(g) + 3B(g) -> 4C(g) 2. 2A(g) + B(g) -> 4C(g) 3. 2A(g) + 2B(g) -> 3C(g) 4. 2A(g) + B(s) -> 3C(g) Remember that a system that does work on the surroundings has a negative value for work (w).

Determination of Boiling Point

I could use help with a few questions... Just a few sentences each: 1. What does it mean to say that the melting point of a pure substance is a characteristic property of the substance? 2. Will the presence of an impurity in a sample cause the melting point of the sample to increase or decrease? Explain. 3. What is mea

Standard Enthalpy of Reaction Question

A 2.50-g sample of powdered zinc is added to 100.0 mL of a 2.00-M aqueous solution of hydrobromic acid in a calorimeter with a total heat capacity of 448 J/K. The observed increase in temperature is 21.1 K at a constant pressure of one bar. Using these data, calculate the standard enthalpy of reaction.

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

Calcium carbide (CaC2) reacts with water to form acetylene (C2H2) and Ca(OH)2. From the following enthalpy of reaction data, calculate ^Hof for CaC2(s): CaC2(s) + 2H2O------> Ca(OH)2(s) + C2H2(g) ^Ho= -127.2kJ What Thermodynamic Quantities do I use? What are the steps to the equation? Please show all of your work

change of enthalpy by dissolving ammonium nitrate

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

Finding the pressure where ozone formation will be spontaneous

In the upper atmosphere, ozone is produced from oxygen gas in the following reaction: 3O2(g) ---> 2O3(g) dG = 326 KJ dH= 285 KJ dS = -141 J/K Assume an atmosphere where p(O2) = 0.140 atm, and where T = 298K. Below what pressure of O3, will ozone production be spontaneous? (Answer in atm)

Free Energy Change Estimation

Estimate the free energy change (Î"Grxn) for the following reaction at 298 K, if each v is present at p = 0.40 atm. N2(g) + 3H2(g) <==> 2NH3(g). Calculate the answer in KJ

Sample Physical Chemistry Problems

1) Ca(s) + 2H20(l) Ca(OH)2(OH)2(aq) + H2(g) 75.0g of Ca(AW = 40.08) are reacted with 40.0 H20 (MW = 18.02) according to the above equation if 30.0 L of H2 (g)(MW = 2.016) are produced at 20 0C,Calculate the pressure of H2 gas. 2) Calculate the heat released when 84.5g of SO2 (MW = 64.07) are used up according to the

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

Distillation lab setup

1. Does the vapor pressure of a liquid change with temperature and if so, why? 2. When attaching the hoses for the cooling water in the distillation apparatus, does the water enter at the top of the condenser and exit at the bottom or enter at the lower end and exit at the upper end? 3. Why is it necessary to add a boilin

Purity of Samples for Melting Points

The sample that you are sure is Tigerium, which is melting range of 145-146 Ë?C. a. Suppose you run your sample of Tigerium and observe a melting range of 145-151 Ë?C. Is your sample impure, or did you heat too fast? b. Suppose you run your sample of Tigerium and observe a melting range of 139-145 Ë?C. Is your sample impure

boiling point of water

Under what conditions does water boil at exactly 100 degrees Celsius? How frequently are these conditions observed in your environment? How could you raise the boiling point of water? How could you lower it? Can you increase the speed of cooking by increasing the heat? Why or why not? Why does a pressure cooker cook food more