# Scienc

Members

11

## Posts posted by Scienc

### Nucleophilicity

Why does CH3CO2H have a greater nucleophilicity than CH3OH?

### Orbital atomic

An orbital can contain up to 2 electrons, and the electrons and orbitals are described by wave functions, are the 3 wave functions the same? for example, two electrons that are in the psi 2 0 0 orbital do they have the same wave function as that orbital?

### Steam pressure

What does "air is saturated with water" or "air is saturated with something" and how can I relate this to vapor pressure?

### Enthalpy

What is the physical meaning of enthalpy?

### 1. Thermodynamic work

16 minutes ago, joigus said:

I think you're confusing change in volume with change in amount of matter present in your system. Moles are a measure of the number of atomic participants in your system. Volume is very different. Please review your statement so that a proper answer can be given to what's troubling you.

The system, such as you've defined it, is an open system (open to exchanges of both energy and matter).

The volume that 6 moles occupy 134.4l and 12 moles occupy 268.8 moles, since 1 mol = 22.4l, for this the gas needs to expand

### 1. Thermodynamic work

What is the difference between the work done by a gas and the workflow that the same gas performs to exist? why does the variation in the internal energy of the equation dH = dQ + nRT not consider the work done by the gas to exist (working flow) but consumes only the heat transfer?

In the question below, the author considers dU = Q. He performs the calculation of the work done by the gas, separated from the internal energy (with an equation dH = dU + nRT ). If you know that in systems with constant volume dU = Q, but the gas volume varies (From 6 moles to 12 moles of gas), this does not imply an internal energy variation equal to dU = w + q (As stated in the 1st law of thermodynamics) and why consider dU = w + q and not dU = Q **? In practice or in what he did, the logic he did not use was.

Question:

“A constant volume calorimeter showed that the fuel loss in burning 1 mole of glucose is equal to -2559kJ in 298K, that is dU = -2555KJ”

### Enthalpy

14 minutes ago, joigus said:

Outra maneira de dizer: a entalpia é uma função do estado que permite expressar os balanços de calor. O calor não é uma função do estado, mas você pode relacioná-lo com uma função do estado. Algum tipo de "potencial de calor". Isso não é legal? Você deve manter a pressão constante se quiser que ela faça seu trabalho como "potencial de calor".

Isso ajuda?

Thank you.

4 hours ago, sethoflagos said:

A energia interna está principalmente associada ao volume fixo, processos fechados onde dU = CvdT se mantém. A entalpia está associada a processos abertos e de pressão fixa, nos quais dH = CpdT se mantém. Em processos abertos, o fluxo de produtos está sendo executado no espaço já ocupado por outra coisa e essa outra coisa precisa ser movida para outro lugar. O trabalho adicional necessário está contido no termo PV em sua fórmula H = U + PV. Portanto, em experimentos de laboratório de química ou processos industriais, geralmente trabalhamos com alterações de entalpia, em vez de alterações na energia interna. Poderíamos usar o U o tempo todo, mas teríamos que acompanhar todos os termos de PV externos e é fácil perder o um ou dois ímpares.

Existem muitas "rugas" no exposto, mas acredito que você esteja mais interessado na ampla visão geral e, nesse nível, o exposto acima funciona bem para mim. Mais elaboração pode ser encontrada nos livros apropriados.

Thank you.

### Enthalpy

A variation of enthalpy at constant pressure is numerically equal to the variation of heat in a chemical reaction, but what is enthalpy in itself? what is its difference for internal energy, is it calculated as H = U + PV, or does that mean physically?

### 1. Thermodynamic work

Guys, why in physics does the work done by the system have the POSITIVE sign, but in chemistry does the work done by the system have the NEGATIVE sign?

### Equation Thermodynamics

Why does the equation τ = -n.R.T.ln⁡ (v_2 / v_1) only work for reversible processes?

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