Question

Does it really help to run hot water over a tight metal lid on a glass jar before trying to open it? Explain your answer.

Short answer

Yes. You can try to open a tight metal lid of a glass jar just by pouring hot water over it. The thermal expansion helps to loosen the metal lid. Because it is the process in which the metal lid expands in the presence of heat.

Step-by-step solution

Thermal expansion

Thermal expansion is the process that happens when you run the jar under hot water. Thermal expansion is the phenomenon in which material expands when they exposed to heat. When a material is heated, the molecules in it will absorb the thermal energy and it undergoes a rapid vibration. Then such molecules need more space than before, which causes the material to expand.

Expansion of metal lid through thermal expansion

The thermal energy absorbed by the metal lid and glass jar are different so they expand at different rates. Metals are good conductors of heat so that they can absorb thermal energy from hot water more easily than glass, which is a bad conductor of heat. So when you run hot water over a tight metal lid, it allows the glass jar lid to expand.

The metal lid expands very fastly than the glass jar. And there occur a small gap between the lid and the glass jar. This gap grows as the lid expands, finally, the lid will come out from the jar.