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One mole of helium is adiabatically expanded from its initial state $\left({P}_{i},{V}_{i},{T}_{i}\right)$ to its final state $\left({P}_{f},{V}_{f},{T}_{f}\right)$. The decrease in the internal energy associated with this expansion is equal to

(1) ${C}_{V}\left({T}_{i}-{T}_{f}\right)$

(2) ${C}_{P}\left({T}_{i}-{T}_{f}\right)$

(3) $\frac{1}{2}\left({C}_{P}+{C}_{V}\right)\left(Ti-{T}_{f}\right)$

(4) $\left({C}_{P}-{C}_{V}\right)\left({T}_{i}-{T}_{f}\right)$