New answers tagged

0

As to "practical significance", which is the heart of your question: Perhaps you should look to water purification and the heats of dehydration - thereby allowing you to find the most economically viable material route to ultra-purified water. However there exist a huge class of materials called zeolites which may function more efficiently. ...


0

Depending on the constraints you impose on the system, there are different criteria for spontaneity, however, the commonly running theme is that it is related to minimizing some state function. For example, as a simple example from classical mechanics, the time evolution of the system is such that the potential energy of the mechanical bodies is minimized. ...


3

The internal energy $U$ is the sum of all the energies stored in the chemical bonds. If a chemical reaction happens, the bonds are losing or getting energy. Heat is getting in or out of the system, and this heat $\Delta Q$ can be measured. $\Delta U$ =$\Delta Q$, if the volume is constant. But if the transformation is carried out in contact with the ...


0

If your process is not isobaric, there is no way you can consider it as only one hypothetical isobaric step. So you need to 'decompose' your process into more than one steps, and among those several steps, there can be isobaric step. For example, your process of interest is $$(p_1, V_1, T_1) {\rightarrow} (p_2, V_2, T_2) $$ where $p_1 ≠ p_2, V_1 ≠ V_2, T_1 ≠ ...


1

Disclaimer: The below discussion only holds to be completely true for reversible processes and for ideal gases. I think the problem is you're thinking of it the wrong way, that is, you first think that $ q= nC_p \Delta T$ and for constant pressure process $q_p= \Delta H$ , and hence, $ \Delta H = nC_p \Delta T$ In actuality, it is the other way around. ...


0

Since you have the capacity per unit vilume, you don't need to use the density of the solution. Your answer is true. The reaction is (( carbonate + HCl ----> Hydrogencarbonate + cholorid )). Since, all HCl has consumed, the reaction won't preceed more (( I mean that Hydrogencarbonat won't react with HCl, because there is no HCl left )). I think that the ...


1

You could possibly do a formation of a salt using an acid/base reaction, evaporate it, then calculate the heat released when it enters solution. Extra points if you can explain heat lost to the solution in terms of the thermal stability of water. This would give you a more advanced look into the thermal processes of chemistry, its the kind of lab we would do ...


2

You did the right thing. However the method you used sounds confusing sometimes, it gave me a hard time too. Hess's law says that the resultant enthalpy change in a reaction is same whether it occurs in one or several steps . We can use that to our advantage by assuming a hypothetical situation where the given reaction proceed in a number of steps for our ...


3

"Spontaneous" means different things in different contexts Your penultimate paragraph captures a key idea. The explanation for why this is right requires a recognition of the context of the term "spontaneous". The context of the statement at the start of the question $\Delta G=\Delta H-T\Delta S$ is negative is thermodynamic stability. ...


2

Consider a gas which was subjected to two different processes: isochoric and isobaric. Isochoric: If a certain amount of heat $dq$ was given to this gas, then this heat will be completely used up in raising it's temperature since $dw$ is zero. So, $$dq_v = dU$$ Also $$dq_v = nC_v dT$$ where $C_v$ is constant volume molar heat capacity. Therefore we can say ...


1

The heat capacities arise when you define various differential forms of U and H. The differential forms define how the energy responds to changes in thermodynamic variables such as pressure, temperature and volume. For instance, one form for U reads: $$\begin{align}dU = \left(\frac{\partial U}{\partial T} \right)_V dT + \left(\frac{\partial U}{\partial V} \...


1

Principally, definitions cannot be derived. They are chosen. What you have described in the question are heat capacities without the adjective specific, being heat capacities of a whole system. Note that specific heat capacities are related to the substance unit mass amount, mostly 1 kg, so I would expect the mass in denominator, like $$c_V = \frac 1m . \...


2

If a body absorbs a quantity of heat $q$ its temperature will normally rise by a value $\Delta T$. The average heat capacity over this temperature range is defined as $C_{av}\equiv q/\Delta T$. The instantaneous heat capacity at temperature $T$ is $C\equiv dq/dT$. This definition is not exact enough, however, until the path of heating is specified. From the ...


2

The equation $$\ln\left(\frac{k}{T}\right) = \frac{-\Delta H^{\ddagger}}{RT} + \frac{\Delta S^{\ddagger}}{R} + \ln\left(\frac{k_\mathrm{B}}{h}\right)$$ does not assume that $\Delta S^{\ddagger}$ is temperature independent. To evaluate its T dependence you might proceed as follows: $$\left(\frac{\partial \Delta G^{\ddagger} }{\partial T}\right)_p = -\Delta S^{...


Top 50 recent answers are included