解:(1)水吸收的热量$Q_{吸}=c_{水}m_{水}(t - t_{0水}) = 4.2\times10^{3}\text{ J/(kg}\cdot^{\circ}\text{C})\times0.08\text{ kg}\times(18^{\circ}\text{C}-12^{\circ}\text{C}) = 2.016\times10^{3}\text{ J}$
(2)铅块放出的热量$Q_{放}=Q_{吸}=2.016\times10^{3}\text{ J};$铅的比热容$c_{铅}=\frac{Q_{放}}{m_{铅}(t_{0铅}-t)}=\frac{2.016\times10^{3}\text{ J}}{0.2\text{ kg}\times(90^{\circ}\text{C}-18^{\circ}\text{C})}=0.14\times10^{3}\text{ J/(kg}\cdot^{\circ}\text{C})$