In practice, the equation is often integrated between two temperatures under the assumption that the standard reaction enthalpy Δ Δ r H ⊖ ⊖ is constant (and furthermore, this is also often assumed to be equal to its value at standard temperature). Since in reality Δ Δ r H ⊖ ⊖ and the standard reaction entropy Δ Δ r S ⊖ ⊖ do vary with temperature for most processes, the integrated equation is only approximate. Approximations are also made in practice to the activity coefficients within the equilibrium constant.