替える, 換える, and 代える: replacement, exchange, and substitution
Compare three spellings of かえる through bedding replacement, currency exchange, and substitution, tracking both the original item and its replacement.
Replace an item used for the same purpose
汚れたシーツを新しいものに替えました。 says that someone replaced dirty sheets with fresh ones. 替える is used for replacing an item with a new or different one serving the same purpose.
電池を替えても、時計は動きませんでした。 says that the clock did not run even after its battery was changed. Replacement does not establish that the problem was solved.
Exchange for something else
空港でドルを円に換えました。 means that someone exchanged dollars for yen at the airport. ドルを marks the currency given up and 円に the currency received.
換 for exchanging goods or currency can be close in meaning to 替 for replacement. This example changes the currency from dollars to yen, rather than merely replacing worn banknotes.
Let one thing serve in place of another
When distributing material instead of giving a detailed explanation, one can say 資料の配布をもって説明に代えます. This is a relatively formal way to say that the handout distribution will serve in place of an explanation.
The spellings overlap in some contexts and cannot be assigned mechanically to every noun. Learn representative combinations after identifying replacement, exchange, or substitution, and distinguish them from changing a plan in 予定を変える.
In ドルを円に換える, which currency is given up and which is received?
Show the answer and why
Dollars are given up and yen received. を marks the original item exchanged, and に marks the outcome.