Google's Geocoding API has two different types of limits.
The rate limit is the amount of API requests that can be performed within a certain time interval. According to Google's API Usage and Billing page, there is a limit of 50 requests per second. If you exceed this amount, subsequent requests to the API will fail with the
OVER_QUERY_LIMIT status code and the geocoded data will not be returned.
Google might also block your access to the API if you repeatedly go over the limit.
Google generally does not limit the amount of lookups you can perform per account, but they do require you to contact their sales team for volume pricing when expecting more than 500,000 API lookups per month.