.She was too excited to do any housework that morning,for in the evening she would be going to a fancy-dress party with

.She was too excited to do any housework that morning,for in the evening she would be going to a fancy-dress party with her husband.
这里第一句用了that morning,第二句是in the evening 这两个一个用了介词in,一个没有用,有什么区别呢,