Boiling

Boiling is a process of changing liquid into gas. Boiling occurs when the saturated vapor pressure is equal to the air pressure ( air pressure = atmospheric pressure). We only discuss boiling water. The saturated vapor pressure of water is directly proportional to the temperature of the water, the higher the water temperature, the higher the pressure of saturated vapor. When we heat water, small bubbles usually appear on the bottom of the container. The existence of bubbles indicates the change in a liquid into a gas. If the saturated vapor pressure in the bubble is smaller than the outside air pressure, the bubble will shrink and disintegrate before arriving at the surface. Bubbles are destroyed because the thrust force of the outer air is higher than the thrust force of the steam inside the bubble. The external air pressure is higher than the vapor pressure in the bubble so that the outside air has a more significant force (P = F / A).

As the temperature of the water increases, the pressure of the saturated vapor in the bubble also increases. If the pressure of the saturated vapor in the bubble is equal to or higher than the pressure of the outside air, then the bubble will expand and float until it reaches the surface. After arriving on the surface, bubbles will break, and the water vapor in the bubble detaches from the water. The boiling process occurs. Bubbles get more prominent because the thrust force in the bubble is higher than the thrust force of the outside air. The vapor pressure in the bubble is higher than the external air pressure so that the steam inside the bubble has a greater force. As the bubbles increase, the volume of steam also increases so that the density of the vapor decreases. Because the vapor density decreases (the density of the vapor is smaller than the density of water) the bubbles can float to the surface. Similar to dry wood or cork that floats on the surface of the water. Dry wood or cork can float because the density is smaller than the density of water.

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Based on the description above, we can say that the boiling process occurs when the water vapor pressure is equal to or greater than atmospheric pressure. Thus, the boiling point temperature of the water is very dependent on atmospheric pressure. The smaller the atmospheric pressure, the lower the boiling point temperature. Or conversely, the higher the atmospheric pressure, the higher the boiling point temperature. Usually the higher a place is measured from the surface of the sea, the smaller the atomic pressure at that place. Therefore it can be concluded that the higher an area is measured from sea level, the lower the boiling point temperature at that place. The boiling point temperature at the hill is lower than the boiling point temperature on the beach. The boiling point temperature at the top of the mountain is lower than the boiling point temperature in the lowlands. Heated water on a mountaintop boils faster than heated water by the beach. But if you cook rice at the top of the mountain, rice is cooked longer because the boiling temperature is low so the boiling temperature is low. To quickly cook, a pressure cooker is usually used. The pressure cooker functions to increase air pressure so that the boiling point temperature becomes higher. High boiling temperature causes high boiling water temperature.

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