Why does evaporation cause cooling?
When a liquid evaporates, its molecules convert from the liquid phase to the vapor phase and escape from the surface. What drives this process is heat. In order for the molecule to leave the liquid surface and escape as a vapor, it must take heat energy with it. The heat that it takes with it comes from the surface from which it evaporated. Since the molecule is taking heat with it as it's leaving, this has a cooling effect on the surface left behind.
The faster molecules, those with more energy, are more likely to escape. This means that the molecules still in a liquid state are the slower ones. The average speed of the remaining molecules is also slower. Thus the temperature of the remaining water is lower. That is why evaporation causes cooling.
When the wind blows on your finger, the hottest, highest-energy molecules evaporate. The water molecules remaining are slower-moving and less energetic. So
the molecules that are left result in a lower average energy, and
therefore a lower temperature. Your finger feels cooler in the
direction of the wind. That why evaporation causes cooling.
As the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases. This phenomenon is also called evaporative cooling.
This is why evaporating sweat cools the human body.
Why does evaporation take place on the surface of the water?
For molecules of a liquid to evaporate, they must be located near the surface, be moving in the proper direction, and have sufficient kinetic energy to overcome liquid-phase intermolecular forces
In an area of less pressure, evaporation happens faster because there is less exertion on the surface keeping the molecules from launching themselves.
Why does the temperature stay constant during freezing point?
The temperature stays constant while a liquid freezes because heat energy is released when the particles slow down to take up fixed and orderly position in the solid.
Why is it that the freezing and melting point of water is the same degrees?
We all know that the melting point of water is 0 °C (32 °F). The freezing point of water is the same as the melting point as ling as the water contains what is called a nucleating substance. , but in the absence of nucleators water can supercool to -42 °C (-43.6 °F) before freezing. It is difficult, if not impossible, to heat a solid above its melting point because the heat that enters the solid at its melting point is used to convert the solid into a liquid. It is possible, however, to cool some liquids to temperatures below their freezing points without forming a solid. When this is done, the liquid is said to be supercooled.
In the presence of nucleating substances, the freezing point of water is the same as the melting point, but in the absence of nucleators, water can supercool to −42 °C (−43.6 °F, 231 K) before freezing.
Science Report: The Leech “Leeches are touted as ‘terrors of the jungle’,” my neighbour’s son told us after his army training in Brunei recently. His body has all the marks which he claimed are the “work of the leeches”. This prompts me to do a research on leeches. There are about 650 species of leeches worldwide. Not all of them suck blood for sustenance. They can strike fear into the hearts of trekkers who invade their habitats. The leech analyses its environment with its impressive array of sensors for a good meal, in this case, animal and human blood. Some feed on worms, snails and insect larvae. Others are vegetarian and feed on organic debris. I shall focus on leeches, which sucks blood as they hold many medicinal secrets, earning them the title of ‘physicians’. Since ancient times, leeches have been used in bloodletting by various civilizations. It was believed that certain health disorders were caused by bad blood, which could be removed by the leech. Unfortunately, for the patient, bloodletting was supposed to be beneficial only when performed up to the point of fainting. Therefore, the patient might find himself plastered with up to fifty leeches, a feat certainly not for the faint hearted. A full meal for a leech only extracts about 5 millilitres but the resultant loss of blood from the wound can extend to 150millilitres. Modern science now utilized leeches in plastic surgery and reconstructive microsurgery involving the attachment or reattachment of body parts. Leeches could alleviate venous congestion. True leeches have hind suckers for attaching themselves to the skin of their victims and a fore sucker for drawing blood. Aquatic leeches may feed on the blood on the blood of fishes, amphibians, birds or mammals, while land leeches only feed on the blood of mammals. The feeding process is an art in efficiency. Unless disturbed, the leech can guzzle a few times its body weight of blood before dropping off and happily resting until its next meal in a few months time. Without the biochemical compounds secreted by the salivary glands during feeding, the leech will not survive successfully as humans and animals do not like to give up their blood. The first line of defence for the leech is stealth in the biochemical sense. The breach of the skin surface is almost painless (otherwise it will be a nightmare for a patient undergoing leech therapy). Thanks to an anaesthetic in the leech’s saliva, its blood sucking goes undetected. When we suffer a cut, we do not bleed to death because the blood clots. If left uninterrupted, blood can clot in about 10 minutes, presenting a major obstacle to the leech during feeding which may take about thirty minutes. Therefore, a leech is armed with various countermeasures to disrupt this clotting process at a minimum of seven different points. Blood will continue to ooze from the biting site for a few hours even if the leech had his fill and ditched its host. This is made possible as the leech saliva has an anticoagulant (blood thinning agent), hirudin, which blocks thrombin, the enzyme initiating the clotting process. So next time in the jungle, before you raise a hand to strike off this annoying pest, stop and ponder about the wondrous biochemical compounds in the leech, a veritable medicine packed in into a tiny critter. A wealth of medicinal secrets can hopefully be unraveled from further research and study by scientists. Or perhaps simply appreciate the leech for its remarkable methods of survival, forged from the crucible of evolution.
When a liquid evaporates, its molecules convert from the liquid phase to the vapor phase and escape from the surface. What drives this process is heat. In order for the molecule to leave the liquid surface and escape as a vapor, it must take heat energy with it. The heat that it takes with it comes from the surface from which it evaporated. Since the molecule is taking heat with it as it's leaving, this has a cooling effect on the surface left behind.
The faster molecules, those with more energy, are more likely to escape. This means that the molecules still in a liquid state are the slower ones. The average speed of the remaining molecules is also slower. Thus the temperature of the remaining water is lower. That is why evaporation causes cooling.
When the wind blows on your finger, the hottest, highest-energy molecules evaporate. The water molecules remaining are slower-moving and less energetic. So
the molecules that are left result in a lower average energy, and
therefore a lower temperature. Your finger feels cooler in the
direction of the wind. That why evaporation causes cooling.
As the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases. This phenomenon is also called evaporative cooling.
This is why evaporating sweat cools the human body.
Why does evaporation take place on the surface of the water?
For molecules of a liquid to evaporate, they must be located near the surface, be moving in the proper direction, and have sufficient kinetic energy to overcome liquid-phase intermolecular forces
In an area of less pressure, evaporation happens faster because there is less exertion on the surface keeping the molecules from launching themselves.
Why does the temperature stay constant during freezing point?
The temperature stays constant while a liquid freezes because heat energy is released when the particles slow down to take up fixed and orderly position in the solid.
Why is it that the freezing and melting point of water is the same degrees?
We all know that the melting point of water is 0 °C (32 °F). The freezing point of water is the same as the melting point as ling as the water contains what is called a nucleating substance. , but in the absence of nucleators water can supercool to -42 °C (-43.6 °F) before freezing. It is difficult, if not impossible, to heat a solid above its melting point because the heat that enters the solid at its melting point is used to convert the solid into a liquid. It is possible, however, to cool some liquids to temperatures below their freezing points without forming a solid. When this is done, the liquid is said to be supercooled.
In the presence of nucleating substances, the freezing point of water is the same as the melting point, but in the absence of nucleators, water can supercool to −42 °C (−43.6 °F, 231 K) before freezing.
Science Report: The Leech
“Leeches are touted as ‘terrors of the jungle’,” my neighbour’s son told us after his army training in Brunei recently. His body has all the marks which he claimed are the “work of the leeches”. This prompts me to do a research on leeches.
There are about 650 species of leeches worldwide. Not all of them suck blood for sustenance. They can strike fear into the hearts of trekkers who invade their habitats. The leech analyses its environment with its impressive array of sensors for a good meal, in this case, animal and human blood. Some feed on worms, snails and insect larvae. Others are vegetarian and feed on organic debris.
I shall focus on leeches, which sucks blood as they hold many medicinal secrets, earning them the title of ‘physicians’. Since ancient times, leeches have been used in bloodletting by various civilizations. It was believed that certain health disorders were caused by bad blood, which could be removed by the leech.
Unfortunately, for the patient, bloodletting was supposed to be beneficial only when performed up to the point of fainting. Therefore, the patient might find himself plastered with up to fifty leeches, a feat certainly not for the faint hearted. A full meal for a leech only extracts about 5 millilitres but the resultant loss of blood from the wound can extend to 150millilitres. Modern science now utilized leeches in plastic surgery and reconstructive microsurgery involving the attachment or reattachment of body parts.
Leeches could alleviate venous congestion. True leeches have hind suckers for attaching themselves to the skin of their victims and a fore sucker for drawing blood. Aquatic leeches may feed on the blood on the blood of fishes, amphibians, birds or mammals, while land leeches only feed on the blood of mammals.
The feeding process is an art in efficiency. Unless disturbed, the leech can guzzle a few times its body weight of blood before dropping off and happily resting until its next meal in a few months time. Without the biochemical compounds secreted by the salivary glands during feeding, the leech will not survive successfully as humans and animals do not like to give up their blood. The first line of defence for the leech is stealth in the biochemical sense. The breach of the skin surface is almost painless (otherwise it will be a nightmare for a patient undergoing leech therapy). Thanks to an anaesthetic in the leech’s saliva, its blood sucking goes undetected. When we suffer a cut, we do not bleed to death because the blood clots. If left uninterrupted, blood can clot in about 10 minutes, presenting a major obstacle to the leech during feeding which may take about thirty minutes.
Therefore, a leech is armed with various countermeasures to disrupt this clotting process at a minimum of seven different points. Blood will continue to ooze from the biting site for a few hours even if the leech had his fill and ditched its host. This is made possible as the leech saliva has an anticoagulant (blood thinning agent), hirudin, which blocks thrombin, the enzyme initiating the clotting process.
So next time in the jungle, before you raise a hand to strike off this annoying pest, stop and ponder about the wondrous biochemical compounds in the leech, a veritable medicine packed in into a tiny critter. A wealth of medicinal secrets can hopefully be unraveled from further research and study by scientists. Or perhaps simply appreciate the leech for its remarkable methods of survival, forged from the crucible of evolution.