exchange

1. Origins, structure, and basic meaning

• Structure: 換 has 12 strokes and the on-reading かん. 換える (かえる) describes changing something; 換わる (かわる) describes something changing into another form.
• Basic usage: These words occur in replacing air and exchanging money or points for another form.

2. Common pitfalls and similar expressions

• What is exchanged and the result
  • 紙幣を硬貨に換えてもらった means having a banknote exchanged for coins. The item before を is the original object; the item before に is the result.
  • 紙幣に換わった describes coins becoming a banknote. In 点数が店の商品券に換わる, collected points become store vouchers.