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enthalpy change formula

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From Wikipedia

Enthalpy change of solution - Wikipedia, the free encyclopedia

The enthalpy of solution, enthalpy of dissolution, or heat of solution is the ... potassium chlorate, +41.38. acetic acid, -1.51. sodium hydroxide, -44.51 ...


From Yahoo Answers

Question:IS THERE A FORMULA RELATING THE ENTHALPY OF REACTION WITH THE ACTIVATION ENERGY?

Answers:Not really. If you can get the activation energy of the forward and reverse reactions, the difference between the two will be the enthalpy of the reaction. But enthalpy of reaction and activation energy operate in two realms, one being in thermodynamics, the other being in kinetics.

Question:My reaction consisted of 0.05g of Mg(s) + 5g of HCl(l) 1M . At the start of my reaction the temperature was at 16.86C and at the end (when i saw that all the reactants had been used up) the temperature was at 40.66C. Is there anyway that i can figure out the activation energy and change in enthalpy for this reaction so that i might be able to put it into an energy profile graph?

Answers:q = mc T q= enthalpy change m = mass of the water c= specific heat T = temperature change in C we must 1st find the mass of water so we have 5gof HCl in 1M solution 5g / 36.5g/mole = .137moles the ration of moles to liters is 1:1 so we have .137 liters of water which weights 137g (we'll assume the HCl does not affect the specific heat) q = 137g x 4.18j/g C x (40.66 - 16.86) q =137g x 4.18j/g C x 23.8 C q = 572.66j/ C x 23.8 C q = 13629.3j 13629.3j was absorbed by the water so therefore 13629.3j was released so H = -13629.3j as far as activation energy i need to read on it more but there's your enthalpy change

Question:The activation energy for a reaction in the forward direction is 78 kJ. THe activation energy for the same reaction in reverse is 300 kJ. If the energy of the products is 25 kJ, then: A) What is the energy of the reactants? B) What is the enthalpy change for the forward reaction? --- it would be appreciated if you could also explain the approach to the problems. THANKS

Answers:Draw a potential energy diagram. Something like this.http://www.bbc.co.uk/scotland/education/bitesize/higher/img/chemistry/calculations_1/pe_diags/fig10.gif Now I assume when they say "the energy of the products is 25 KJ" they're talking about the forward reaction. So if the products are at 25 KJ and the activation energy of the reverse reaction is 300 KJ then the peak is at 300+25=325 KJ. Now if the activation energy of the forward reaction is 78 KJ then that means it takes 78 KJ for the forward reaction to get to the peak at 325 KJ so then the forward reaction must have started at 325-78=247 KJ. That answers question A. A) 247 KJ B) H=energy of products minus energy of reactants =25 KJ-247 KJ=-222 KJ Here's a badly drawn potential energy diagram to help you understand. http://s171.photobucket.com/albums/u293/jfdnew/?action=view¤t=potentialenergydiagram.jpg There you go. :)

Question:

Answers:AE: is the amount of energy needed to give to an element to start the actual reaction, Entalphy change however is the diffrence between (heat) energy levels of reactants and products. if ure still stuck with it check out the link below, :)

From Youtube

Enthalpy Changes for Chemical Reactions :General Chemistry lecture covering endothermic and exothermic reactions, Hess Law, bond energies, and standard enthalpies of formation for chemical substances. We also describe the method of calculating the enthalpy of combustion for materials.

Enthalpy of Expansion and Compression of Gases :General Chemistry lecture covering the basic transfer of heat and work to and from gases during expansion and compression. We discuss how to compute heat and/or work for isochoric heating, isothermal expansion and adiabatic expansion. We also present a general strategy for determining changes in thermodynamic state functions for arbitrary changes in pressure, volume and temperature for ideal gases.