题干

油锅着火能用水扑灭吗?某科普类节目曾演示过一个模拟实验:将锅中的油加热到燃烧后,身穿防护服的消防员将一瓶水倒入油锅中,在水倒进锅里的一瞬间,热油飞溅,巨大的火苗窜起一米多高.请用所学的知识加以解释。

上一题 下一题 0.0难度 选择题 更新时间:2016-04-18 06:26:11

答案(点此获取答案解析)

①燃烧的条件

②水的密度比油大,水加入后,会沉在油的下方,起不到隔绝氧气作用。

③油锅的温度很高,水加进去之后容易汽化,水汽化过程将油滴带出,增加油与氧气的接触面积,使燃烧更剧烈。

示例:可燃物燃烧必须具备两个条件:一是与助燃剂(氧气)充分接触,二是温度达到着火点。当水倒入燃烧的油锅时,因为水的密度比油大,水无法覆盖在油的表面,起不到隔绝氧气作用。油浮在水面上继续燃烧,在高温下,水迅速汽化过程中携带着油滴冲出油锅,大量的油滴与空气(氧气)充分接触,引发更剧烈燃烧,产生大量的热。

同类题4

阅读理解

    Jaden Hayes first lost his dad when he was four and then last month his mom died unexpectedly in her sleep.

    “I tried and I tried to get her awake—I couldn't,” said Jaden.

    Jaden is understandably heartbroken. But there's another side to his sadness. When he first made public a few weeks ago he told his aunt, and now guardian, Barbara DiCola, that he was sick of seeing everyone was sad all the time. And he had a plan to fix it. He asked his aunt Barbara to buy a lot of little toys and bring him to downtown Savannah, so he could give them away.

    “I'm trying to make people smile,” said Jaden. He gave his toys to people who weren't smiling and then turned their day around. He has gone out on four different occasions now and he is always successful, though sometimes he doesn't get exactly the reaction he was hoping for.

    It's just so unexpected to some people that a six-year-old child would give away a toy— expecting nothing in return—except a smile. Of course he is paid beautifully in hugs and his aunt says the reactions have done wonders for Jaden, who will then feel joyful.

    “But I'm still sad that my mom died,” Jaden said.

    This is of course not only a fix, but the smiles he has made so far—nearly 500 at last count—Jaden has clearly found a purpose.

    “I'm counting on it to be 33, 000,” said Jaden.

    When asked if he thought he could make that goal, he answered, “I think I can.”