Explain why splashing a small amount of liquid nitrogen (b.p. \(77 \mathrm{~K}\) ) is not as harmful as splashing boiling water on your skin.

When a liquid transforms into a gas, it absorbs energy from its surroundings. This energy is what we call the latent heat of vaporization. It's essential for understanding why boiling water can cause severe burns, while liquid nitrogen may not immediately harm your skin. As the liquid nitrogen comes in contact with your skin, it requires a substantial amount of energy to vaporize. This energy is pulled from your skin, causing the surrounding skin temperature to drop. Liquid nitrogen, with its low boiling point, vaporizes almost instantly when encountering your warm skin. However, because it vaporizes so quickly, the heat transfer is less, causing less injury.

For instance, when you shower with hot water, the heat is not just lost to the air; some of it is actually being used to convert the water on your body into steam. This is why steam rooms or saunas feel so hot, even though the air temperature might not be as high as the water's temperature in a hot shower.

The boiling point of a substance is the temperature at which it transitions from liquid to gas. At this threshold, the internal pressure of the liquid equals the surrounding atmospheric pressure. For liquid nitrogen, the boiling point is incredibly low at 77 K, which means in most everyday environments, it will boil swiftly, forming a vapor layer. This is a stark contrast to water, which has a boiling point of 100°C (or 212°F) at sea level.

Understanding the boiling point can help explain safety measures in various situations. For example, when cooking, you handle boiling water with caution to avoid burns, while in industrial applications, knowing the boiling point of different chemicals can prevent accidents. The contrasting boiling points of water and liquid nitrogen are critical when considering their interactions with human skin and the different outcomes.

Heat transfer is the movement of thermal energy from one object or substance to another. It can occur through conduction, convection, or radiation. In the case of splashing liquid nitrogen or boiling water on your skin, the heat transfer we're most concerned with is conduction, the transfer of heat through direct contact.

With liquid nitrogen, the Leidenfrost effect is an intriguing example of heat transfer regulation. When it touches the skin, the rapid vaporization forms a protective gas layer that insulates and limits the rate of cooling. Boiling water, on the other hand, doesn't create such a layer, so it remains in prolonged contact with the skin, leading to a continuous and more severe transfer of heat, which can result in significant burns.