I'd use "occurs" and "happens".

Student or Learner
What verb would you use with "chemical reaction"?
"This chemical reaction occurs at a high temperature."
I'd use "occurs" and "happens".
... or even just 'there is a chemical reaction between A and B'. Sometimes the abstraction ('something occurring') needn't be introduced at all: 'The exposed surface of the iron reacts with the oxygen in the air to form rust'.
b
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