What is the difference between bronchitis and pneumonia on an xray?

See below: Bronchitis is an inflammation of the bronchi (tubes which carry air to either the left or right lung). This is typically viral in origin. Bronchitis may not be visible on chest x-ray. Pneumonia is caused by an infection in the lung itself, not the tubes. This can be referred to as an "infiltrate" or "consolidation" and reflects buildup of puss and edema where infection has occurred.

Location...: Bronchitis is due to an infection of the airways and it cannot be seen on a chest x-ray. On the other hand, pneumonia is due to an infection of the lung parenchyma itself and this can be visualized by your doctor on a chest x-ray. So, if the chest x-ray is ok, bronchitis becomes more likely.