Answer
$\Delta E_{int}=50J$
Work Step by Step
We know that;
$\Delta E_{int}=nC_v\Delta T=\frac{5}{2}nR\Delta T$.....eq(1)
We also know that;
$Q=nC_p\Delta T=\frac{7}{2}nR\Delta T$......eq(2)
Dividing eq(1) by eq(2), we obtain:
$\frac{\Delta E_{int}}{Q}=\frac{5}{7}$
$\Delta E_{int}=\frac{5}{7}Q$
We plug in the known values to obtain:
$\Delta E_{int}=\frac{5}{7}(70)=50J$
