熱力學定律

ΔE = q + w

ΔE = ΔH and ΔH = qp

With systems at constant pressure (P) then:

ΔE = q + w

ie. the change in internal energy of a system is equal to the

energy that passes into the system as heat or as work

Where H = enthalpy and is effectively equivalent to the heat supplied to

the system (at constant pressure) ie qp

Δ indicates a change is determined from the difference between the

final and initial state

Conservation of energy:

the change in system’s energy is balanced by an equal and opposite

change in the energy of its surroundings.

Note: if heat or work is transferred out of the system into the surroundings

this is indicated by giving the quantity a negative sign. The sign only

indicates the direction of energy flow

Update:

Rating
• 9 years ago

ΔE是內能

Q是熱能

W是作功

單單從公式上來看

內能就是熱能和功的總和

先來講熱

放熱的時候內能會減少

所以熱能會小於零,吸熱的時候則反之

同樣的道理

作功也是如此

ΔE = q + w

ΔE = q - w

這兩條哪一個對?

每一本原文書都不一樣

但是道理是一樣

先看第一條公式

ΔE = q + w

當系統對外作功的時候W<0,當環境對系統作功的時候W>0

記好上面

再來看看第二條

ΔE = q - w

當系統對外作功的時候W>0,當環境對系統作功的時候W<0

解釋物理意義會隨著公式而變

但是存在的真理卻是不變

還是不懂的話

我就非常簡單的說

"當系統對外作功時,內能會減少,當環境對系統作功時則反之"

然後你再仔細比較那兩條公式

再來你可能會問

那考試要寫哪一條?

就像我紅色的字寫出來讓閱卷老師知道就可以

哪一條公式都是對的

端看你怎麼去詮釋它