When a metal is heated its density decreases. There are two sources that give rise to this decrease of ρ: (1) the thermal expansion of the solid and (2) the formation of vacancies (Section 4.2). Consider a specimen of gold at room temperature (20°C) that has a density of 19.320 g/cm3.

(a)Determine its density upon heating to 800°C when only thermal expansion is considered.

(b) Repeat the calculation when the introduction of vacancies is taken into account. Assume that the energy of vacancy formation is 0.98 eV/atom and that the volume coefficient of thermal expansion, αv is equal to 3αl.