Final answer:
Using oil in a hot water bag instead of water would result in ineffective heat retention and potentially damage the bag or pose risks of leaks and burns, as oil has a lower density and specific heat capacity than water.
Step-by-step explanation:
If oil is used in a hot water bag instead of water, several changes will occur due to the properties of oil as opposed to water. Crude oil is less dense than water, which means it will not be as effective at absorbing and retaining heat compared to water.
A hot water bag's purpose is to transfer heat from the water to whatever it comes in contact with, such as your body. Oil's lower heat capacity and higher expansion rate mean it will not only heat up faster but also cool down faster than water, reducing the bag's ability to maintain a consistent temperature over time.
Another important point is that oil could potentially damage the hot water bag material or degrade its quality over time. Oils could also lead to leaks more easily than water, which poses a risk if the bag is used with high temperature, increasing chances of a burn. Additionally, water's high specific heat is the reason it is used; it can store a lot of heat energy, providing prolonged warmth. Oil's comparative lack of specific heat means it won't provide the same level of warmth for as long as water would.