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Hi guys, today we're going to explain the chemical changes and the chemical reactions.

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You know quite a lot about chemical changes now.

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And I want you to have a look at this screen.

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In the screen, apart from me, I'm going to stay here,

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you will have this mind map here, which is the explanation of the whole unit.

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So, we will explain it little by little.

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This is everything you need to know from this explanation.

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And here on the right, you can see the vocabulary that you need to know to understand this lesson.

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So, to start with, let's go with the vocabulary first.

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And let's see.

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The first word is non-reversible.

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No reversible

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What does it mean?

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Look at this symbol

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Este es el símbolo de deshacer de los ordenadores

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So, something non-reversible

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It means que no puede ser deshecho

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No es reversible

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Second word

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Absorbed

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Absorber

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Release

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Expulsar

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Combustion

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which is the same as burning

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and means both of them combustion

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combustion o quemado

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and finally fuel

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combustible

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sometimes it's used also as gasolina

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so if you look at the words

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you've got also some drawings

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that may help you to understand the meaning.

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And pay attention to the pronunciation too, please.

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So once we know this, we can continue with the explanation.

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First of all, chemical changes.

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Chemical changes are non-reversible.

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They cannot be undone.

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No pueden ser desechos.

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So, for example, if I got these popcorns, if I have the corns, los granitos de maíz, I put them in the microwave when they are inside the package.

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And with the heat of the microwave, they change and we get these popcorns.

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You cannot have the corns as they were before because it happened a chemical reaction.

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So, this means that the atoms in the substances rearrange, se reorganizan, to form new substances.

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Suceden una serie de cambios en las sustancias que crean una nueva sustancia

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y lo que ha sucedido es que sus átomos se han reordenado, reorganizado.

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so all this process we are talking about

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the process is called chemical reaction

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the process of combining two substances

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to get a new one

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a new substance with different properties

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ok

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so this is the main part of the lesson

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the chemical reactions

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but you need to know

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there are two types of chemical reaction.

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The first one is endothermic

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and the second one is exothermic.

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Endothermic refers to the inside.

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It refers to absorb heat.

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O sea que una reacción química endotérmica

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es aquella en la que se absorbe calor.

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A good example of this

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is the photosynthesis that happens with the plants.

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The plants, they get, they absorb the heat

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to produce a chemical reaction to get the food.

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This is endothermic chemical reaction.

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And on the other side, we have exothermic.

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Es aquella en la que se expulsa calor.

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The exothermic release heat.

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Si se expulsa calor, this means that thermal energy is produced.

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Thermal energy, energia calorífica.

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For example, digestion is an example of exothermic chemical reaction.

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The temperature of our body increases during digestion.

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or explosion or

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the most representative of this exothermic

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chemical reaction is

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combustion. Conversion is an exothermic.

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In combustion, you can see

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the examples at page 12, you need

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always oxygen plus

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a fuel, fuel was combustible, o sea que si combinamos un combustible y oxígeno, we get

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thermal energy, que es lo mismo que calor, ok?

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So, you can look up the ways of getting hot or thermal energy, there are three good examples

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in the book, so if you want you can stop the video, have a look at the examples and then

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you continue watching the video but remember that oxygen is always necessary that's why

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i recommend you to do the experiment that you have at page 13 the exercise for and see what happens

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for example i want to show you here i'm gonna do now combustion with the candle i need

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a fuel and I need also

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oxygen and with this I produce

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thermal energy

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but sometimes when we produce

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thermal energy we are happy

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because normally we burn things or we

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do combustion to produce thermal energy to cook

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to heat our houses or i don't know to to be able to move our cars or the buses the transports

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but with that combustion we produce other substances and these substances are not so good

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Why? Because they produce, in the combustion, we can produce carbon dioxide particles,

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a sulfur dioxide that can damage the environment.

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So let's see here an example.

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Let's keep this here so you can see this better.

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One effect that these substances can cause is the global warming, el calentamiento global.

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Carbon dioxide in the atmosphere can cause global warming.

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Another one is that these particles, which is the pollution, la contaminación, can cause respiratory illnesses to the human beings.

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and the third one sulfur dioxide can be mixed with the rainwater and produce the acid rain

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that damages also the environment so i have led to you in the

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in google classroom and in the website i'm gonna let you a document with some videos about global

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warming and acid rain they are very interesting they are from national geographic they have

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subtitles and they are a very good explanation of these bad consequences of combustion

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so this is all for today guys i hope you understood if not we will see each other i hope

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thursday and we can you can ask me questions in the video llamada okay see you soon