In this video we are going to look at exothermic and endothermic reactions.
在本期视频中 我们来看看吸热反应和放热反应
So what are they? how are they different?
它们是什么 有何不同
What about their energy levels?
它们的能量水平如何
In the next couple of minutes you’ll know everything you need to get started.
接下来的几分钟 你将知道最初要了解的一切
An exothermic reaction gives off energy to the surroundings,
放热反应向外界释放能量
like this fire giving off heat.
例如 火释放热量
Whereas an endothermic reaction takes in energy from its surroundings,
而吸热反应从外界吸取能量
like this pool melting snowman taking in the heat.
就像这个可怜的雪人在高温下融化
Just remember Exo means external so giving out,
只需要记住 放热反应就是释放即给出
Endo means internal so taking in.
吸热反应就是向内即吸收
Let’s start by having a quick look.
下面我们快速了解一下
Because exothermic reactions transfer energy to the surroundings
因为放热反应是向外界传递能量
and this energy is usually heat energy.
而且这种能量一般是热量
They cause the surroundings to heat up
它使外界变热
Just like a bonfire keeping everyone warm.
例如 篝火使人温暖
Other examples of exothermic reactions are
放热反应的例子还有
the neutralization reactions between acids and alkalis,
酸碱中和反应
the reactions between water and calcium oxide and respiration.
水与生石灰的反应以及呼吸作用
It is easy to detect exothermic reactions
探测放热反应非常容易
Just get your thermometer and see if the temperature increases
只要测量温度是否升高即可
Watch the hydrochloric acid and sodium hydroxide solution being mixed
观察盐酸和氢氧化钠混合
and see how the thermometer increases
然后看温度的增高便可得出
most chemical reactions are exothermic because heat is given out
多数化学反应释放能量所以为放热反应
physical processes can also be endothermic or exothermic
物理过程可以是吸热反应或放热反应
When something freezes it goes from liquid to solid
某物结冰时就是从液态转为固态
Bonds need to be made for this to happen
这一切的发生首先要建立某种连接
and to make bonds you need to do some work
而为建立这种连接 你需要做点功课
Thus energy is given out and freezing is exothermic
凝固是能量的释放 因此是放热反应
Similarly when condensation happens because a gas is going to liquid
同样的 凝结的发生是因为气态变为了液态
Again bonds need to be made
这种连接再次形成
so energy is given out
这里仍旧是热量释放
so freezing and condensation are both exothermic
因此凝固和凝结都是放热反应
Because in exothermic reactions energy is given out to the surroundings
因为放热反应中 能量释放到外界
This means that energy of the reactants is higher than the energy of the products
这意味着反应物的能量高于产物的能量
hence the energy curve for the exothermic reactions will look like this
因此放热反应能量曲线看起来是这样的
Now let’s have a look at endothermic reactions
下面我们一起看看吸热反应
These are less common
吸热反应并不常见
Remember that endothermic reactions take in energy from the surroundings
记住吸热反应从外界吸收能量
Again as with exothermic reactions the energy being transferred is usually heat
与放热反应一样 其实质都是热量的转移
So in endothermic reactions the surroundings usually get colder
因此吸热反应常常使外界变冷
Again, we can detect endothermic reactions with a thermometer
同样 我们可以用温度计测量放热反应的温度变化
because the temperature would get colder
因为温度会降低
some examples of endothermic reactions are electrolysis
常见的吸热反应有电解
the reaction between sodium Carbonate and ethanoic acid and photosynthesis
碳酸钠和醋酸的反应以及光合作用
Endothermic reactions can also be seen in physical processes
吸热反应也可见于物理变化
where something melts it goes from a solid to a liquid
融化即物质由固态变为液态
For this to happen bonds need to be broken
它的发生需要破坏掉这种些连接
and to break bonds energy to be put in like our melting snowman
继而能量流入 例如我们融化的雪人
Boiling is also endothermic
沸腾也是吸热反应
because energy needs to be put in to break the bonds from liquid to turn to gas
因为从液体变为固体需要输入能量使连接断裂
because in endothermic reactions energy is added to the reaction
因为吸热反应需要注入能量
the energy of the products is higher than the energy of the reactants
产物比反应物能量高
So the energy curve looks like this
能量曲线如图
so there you have exothermic and endothermic reactions
到这儿 你就学完了放热反应和吸热反应
All you need to remember is that exothermic reactions give out energy
你需要记住的就是 放热反应是释放能量
endothermic reactions take in energy
吸热反应是吸收能量
both can be detected with a thermometer
它们都可以用温度计测量出
In exothermic reactions the surroundings get hotter
放热反应时 外界变热
and in endothermic reactions the surroundings get colder
吸热反应时 外界变冷
exothermic reactions start with more energy and end with less
放热反应能量由高到低
while endothermic reactions start with less energy and end with more
而吸热反应 能量由低到高
Freezing and condensation are exothermic
冷冻和冷凝是放热反应
because bonds need to be made which gives out energy
因为建立某种连接会释放能量
Melting and boiling are endothermic
融化和沸腾是吸热反应
because bonds are broken which requires additional energy
因为连接断裂需要吸收能量
think of the snowman again
雪人就是很好的例子
and finally Exothermic reactions are more common
最后 放热反应更加常见

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