Enthalpy Definition and 68 Threads

Hello PF! I have some questions regarding these concepts. First of all, are the following expressions valid for any case? i.e. any kind of process, like isochoric, isobaric. \Delta U = \int C_v \ dT \Delta H = \int C_p \ dT Or is the ΔU expression only valid when dV = 0, and ΔH when dP = 0...

Homework Statement Initial pressure: 140kPa Temperature: 25C or 298K Volume: 0.14m^3 Final Pressure:1.4MPa or 1400kPa It uses index compression, n=1.25. So PV^1.25 = constant. c_p = 1.041kJ/kg.K and c_v = 0.743 kJ/kg.K Homework Equations ¥ = c_p/c_v ΔS=c_v*ln(Tf/Ti) + R*ln(Vf/Vi) [i...

Homework Statement Consider an ideal gas with C_V=6.76 \frac{cal}{mol \cdot K}. Calculate \Delta H and \Delta U when ten moles of this gas are heated from 273.15 K to 373.15 K. Homework Equations \Delta H = \Delta U + P\Delta V Q=n C_V \Delta T The Attempt at a Solution As I'm given the heat...

Hi I'm new to this site, so I'm not sure where to post this question but chemistry seemed fitting. I'm current taking 2 thermo classes, engineering and chemistry, and I'm having trouble with the concept of enthalpy. This is what I believe I understand. I Hope the following is all correct if...

Why there no change in volume and enthalpy of solution when two components are mixed

Hello I am curious, why is the heat if mixing negative? Why would mixing decrease the enthalpy?

I was recently learning average bond enthalpies and was wondering if it varies at different temperatures. I know that in different molecular configurations, bond strength is affected by the arrangement of the atoms, but at higher temperatures, there is higher vibrational energy, right? So, if we...

I am reading on wikipedia about internal energy and the describe it as the energy required to create a system. Ithought that this was the definiton for enthalpy of formation. Was it meant by the definition of internal energy?

Okay so I think I know what I'm doing, but I have a lab tommorow and I have to use Hess's Law to find the total enthalpy change of Mg(s)+1/2O2(g)-->MgO(s). I know how to do that but during my lab tommorow I have to find the enthalpy change of 2 reactions. First, Mg(S)+2HCL(aq)-->H2(g)+MgCl2(aq)...

Homework Statement Using Hess's Law and any necessary information from your Data Booklet, calculate the molar enthalpy of reaction for the combustion of ethene in kJ/mol. im so lost! i was going to find each sections molar en thalpy and then balance it but what's oxygens and do i multiply...

Hi- I have been working on a problem and cannot figure out the last part. First, I needed to calculate the average pi-bond contribution to the enthalpy for C-C single, double, and triple bonds. Given: C-C single=348, doube=614, triple=839 kj/mol I calculated: 839-614=225 614-348=226 So the...

ENTHALPY ? Concept Undestanding help Homework Statement Hello, I am studying about enthalpy and I don't need any homework help but what I do desperately need is someone to explain to me how it works. I don't understand what enthalpy is and what the relationship is between heats of reactions...

Homework Statement I need to find a theoretical enthalpy for a reaction so that I can find a percent error. the reaction is: CaCl2+H20 =>Ca)+2HCl Homework Equations delta H=m*c*delta T The Attempt at a Solution Should I use the enthalpies of formation for each of the products?

Can someone help me understand this: By salting the crushed ice, the beer got cold faster. Why?! I have recently studied some Enthalpy, so if anyone could give me an explanation to this using anything related to Enthalpy I'd be very grateful!

Im in a gr 12 chemistry course this is a pretty basic question. What is the formula for calculating enthalpy change and molar enthalpy change? i know the molar enthalpy change is H=(mct)/n would the enthalpy change just be H=mct?

Well, my chemistry teacher is extremely confusing, and wants us to create our own lab where we figure out the enthalpy changes in a chemical reaction. Is there are reaction out there that would give a considerable change in temperature, while using chemicals typically found in a high school? As...

Genrerally it's so that hot air has larger enthalpy value than cold air. But is it also so that if you cool air and add water to it at the same time, the enthalpy will stay the same? How will the temp of the water affect the situation?

Hello. Could anyone help me out with a question I'm stuck on? Thanks in advance. Calcium metal reacts with hydrochloric acid in a calorimeter and the enthalpy change is determined. Similarly, the enthalpy change for the reaction of calcium oxide with hydrochloric acid is determined. What...