Impossibility of performance renders agreements void and may require compensation when the promisor knew the impossibility. Agreements to perform acts impossible in themselves are void; contracts that become impossible or unlawful after formation become void when impossibility or illegality occurs. If the promisor knew, or with reasonable diligence might have known, of the impossibility or unlawfulness while the promisee did not, the promisor must compensate the promisee for losses caused by non performance.