There will be fill in the blank with these:
* Exothermic: thermal energy produced/given out (boiling water cooling down) energy at the end increases
* Endothermic: thermal energy taken in (ice melting, taking the heat in to turn into a liquid)energy at the end decreases
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* Exothermic: a reaction or process that releases thermal energy
* Endothermic: a reaction or process that absorbs thermal energy from surroundings
Specified:
* Endothermic reactions: chemical reactions that absorb thermal energy from their surroundings.
* Endothermic Process: thermal energy is absorbed from surroundings, but no new product is formed.
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* Reaction: when substances react together to form a new product
* Process: no new product is made
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* Exothermic examples in everyday life: self heating food, hand warmer.
* Endothermic examples in everyday life: sour candy (sherbet sweets, to be exact).
* Exothermic reaction examples: burning wood, burning a candle, fireworks exploding
* Exothermic processes examples: freezing water into ice, condensation of steam into water
* Endothermic reaction examples: photosynthesis, cooking an egg.
* Endothermic processes examples: melting ice, boiling water, evaporation of water
Memorize one process and one reaction, any of the above examples
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1. Melting → endothermic
2. Evaporation → endothermic
3. Freezing → exothermic
4. Condensing → exothermic
(there will be match the line to endo/exothermic)
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ALL REACTIONS YOU NEED TO KNOW (they will give examples and tell you to fill in blanks)
1. metal + oxygen → metal oxide
2. metal + chlorine → metal chloride
3. metal + sulfur → metal sulfide
4. metal + water (liquid) → metal hydroxide + hydrogen
5. metal + water (gas) → metal oxide + hydrogen
6. metal + acid → salt + hydrogen
Examples for number 6:
* If it is: metal + hydrochloric acid → metal chloride + hydrogen
* If it is: metal + sulfuric acid → metal sulfate + hydrogen
* If it is metal + nitric acid → metal nitrate + hydrogen
8.1 Exothermic reactions
Burning
* Burning is a chemical reaction where a substance combines with oxygen, causing energy changes.
* Burning needs: fuel, oxygen, heat (triangle)
* The substance that reacts with oxygen is called a fuel.
* Fuels store chemical energy (e.g., charcoal, wood, coal, natural gas, oil).
* When a fuel burns, chemical energy is converted to thermal, light, and sound energy.
* Combustion is another name for burning.
Burning Other Substances
* The combustion of hydrogen is an exothermic reaction.
* Hydrogen and oxygen combine to form water.
* As atoms rearrange and combine, energy is released as kinetic, sound, thermal, and light energy.
* Burning other substances in air, like magnesium, is also exothermic.
* Burning magnesium forms magnesium oxide, releasing heat and light as atoms rearrange.
Exothermic Reactions with Water
* Reaction between potassium and water, atoms rearrange to form potassium hydroxide and hydrogen.
* Stored chemical energy is converted into thermal energy.
Exothermic Reactions with Acid
* When magnesium reacts with hydrochloric acid, the test tube gets hot.
* The reaction is exothermic as chemical energy is converted into heat energy.
8.2 Endothermic reactions
* The temperature after an endothermic reaction is lower than at the start.
* If done in a test tube, the test tube would feel colder after the reaction.
Example: Sherbet Sweets
* Sherbet undergoes an endothermic reaction in your mouth.
* Substances dissolve in saliva and react, causing a cool, fizzy feeling.
Examples of endothermic processes:
* Stirring potassium chloride into water: the beaker gets colder. No new product forms, so it is a process, not a reaction.
* Ice melting: solid ice absorbs thermal energy and changes into liquid water. The solid particles packed tightly take the thermal energy to vibrate faster, loose up, and end up as liquid
* Example exothermic reactions: Self-heating cans of food and drinks use exothermic reactions. (Not much detail here — be careful if asked to explain!)
* Using endothermic processes: Ice packs for injuries use endothermic processes. Stored in a fridge/freezer, then placed on injuries. Heat transfers from the body to the ice pack (thermal energy is absorbed).
Using Exothermic Reactions (Simple Explanation)
Self-heating cans (like for coffee) use an exothermic reaction to warm the drink. Inside the bottom of the can, there are two separate parts:
* One has calcium oxide
* The other has water
A foil separates them. When you press a button, the foil breaks, and they mix. This causes a chemical reaction:
Calcium oxide + Water → Calcium hydroxide + Heat
The heat warms the coffee. These cans are useful in places without power — like camping or emergencies.
Q: Explain why self-heating cans are very expensive.
A: They are expensive because the parts inside must stay sealed to keep the food clean and safe, and making that design costs more.
Q: Explain why a self-heating food container can only be used once.
A: It can only be used once because the chemical reaction happens one time — once the materials mix and react, they can’t be used again.
8.3 Reactions of Metals with Oxygen
Reactions of metals with oxygen:
* Many metals react with oxygen when heated.
* some metals are so reactive, you don't need heat for them to react with oxygen
* Reactivity: metals that react faster with oxygen.
* Example: magnesium reacts faster than iron with oxygen, meaning it is more reactive.
* Reactions between metals and oxygen are oxidation reactions.
Reacting:
* Some metals, like sodium, potassium, and calcium, react quickly with oxygen without heating.
* These metals appear dull when taken from their containers. After cutting, the surface is shiny, but it soon becomes dull as it reacts with oxygen.
* These metals are so reactive that they are stored under oil to prevent reaction with water vapor in the air.
* The metal oxide layer prevents further reaction with air or water vapor.
General word equation: Metal + oxygen → metal oxide.
Some metals, like gold, do not react with oxygen. They are inert →unreactive.
(you have the match stuff to definitions, inert is unreactive. Pure means only one substance. One example of a nonreactive metal is gold/copper)
Reaction between iron and oxygen:
* Rusting occurs when iron reacts with oxygen in damp air.
* The result is iron oxide (rust), an orange-brown solid.
* Equation for rust: Iron + Oxygen → Iron Oxide (you will be asked to write this)
* This reaction only happens when both water and oxygen are present.
* Iron is not very reactive with oxygen, so rusting takes a long time.
What causes iron to rust: Experiment where an iron nail is placed in four test tubes:
This exact thing will be in the exam. They’ll ask you why/why not each tube rusts
1. Test Tube 1: Nail in air, no water. Open to air.
2. Test Tube 2: Nail half in water, open to air. Contains both water and air.
3. Test Tube 3: Calcium chloride in the tube absorbs water, making the air dry. Stoppered tube.
4. Test Tube 4: Has boiled water (to remove dissolved gas), covered with oil to prevent air contact. Stoppered tube.
How can iron be protected:
* Painting: Prevents oxygen from reaching the iron.
* Galvanizing: Covers iron with a layer of zinc to block oxygen contact.
8.4 Reactions of Metals with Water
Reactions
* Reactive metals like sodium and potassium must be stored under oil to prevent reaction with water vapor in the air.
* General Word Equation: for metal and water:
* Metal + Water → Metal Hydroxide + Hydrogen
Reactions of other metals
* Calcium and magnesium are less reactive with water.
* Some metals that don’t react with water may react with steam
* Even magnesium reacts more rapidly with steam than water
* The Word Equation for this is: Magnesium + Water (g) → Magnesium Oxide + Hydrogen
(The (g) shows water is in gas form — steam.)
Look at the example below: Magnesium reacts more rapidly with steam than with water.
* In the experiment, magnesium is heated near ceramic wool soaked in water.
* The heat turns the water into steam (water in gas form), which reacts with magnesium.
* Products: Magnesium Oxide and Hydrogen gas.
* The hydrogen gas released can be burnt.
8.5 Reactions of Metals with Dilute Acid
General Reactions
* When a metal reacts with dilute acid, the products are a salt and hydrogen gas.
* General Word Equation: Metal + Acid → Salt + Hydrogen
* Example: Magnesium + Hydrochloric Acid → Magnesium Chloride + Hydrogen
(Magnesium chloride is the salt formed.)
Reactivity with Acids
* Reactive metals like calcium and magnesium dissolve quickly or fizz when added to dilute acids.
(know the above for the table where you have to fill in the blanks: example - what happens when calcium reacts with dilute acid)
* Unreactive metals like silver, copper, gold, and mercury do not react with dilute acids.
You also need to know: one metal so reactive you cant use it in a classroom:
You can say any one of the three: rubidium, francium, cesium
What Happens During the Reaction
* When a metal reacts with an acid, effervescence (bubbling) occurs as hydrogen gas is released.
* The metal appears to disappear into the solution.
* The other product, a salt, stays dissolved and looks invisible as most salts are colourless and soluble.
* To see the salt, you would need to evaporate the water.
Types of Salts Formed
* Hydrochloric acid → forms chloride salts
* Sulfuric acid → forms sulfate salts
* Nitric acid → forms nitrate salts
Copybook Notes
8.4 (reactions of metal with water)
Just some examples you can review.
* magnesium + water → magnesium hydroxide + hydrogen
* calcium + water → calcium hydroxide + hydrogen
* sodium + water → sodium hydroxide + hydrogen
* potassium + water → potassium hydroxide + hydrogen
Thorough Explanation of Endothermic and Exothermic Reactions:
Exothermic reactions and processes:
* In exothermic reactions/processes, energy is released into surroundings, usually as heat or light.
* This makes the surroundings warmer.
* You can identify an exothermic reaction if you feel heat being given off (like a candle burning or fireworks exploding) or if the temperature around it rises.
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Endothermic reactions and processes:
* In endothermic reactions or processes, energy is absorbed from the surroundings.
* This makes the surroundings cooler.
* You can identify an endothermic reaction if it feels cold, if heat seems to disappear, or if something is being heated (like when cooking an egg or melting ice).
Examples: (my understanding)
* Exothermic. When the thing itself is getting colder and the heat is leaving. Like boiling water cooling. Or when the area around the object is warming up because of the object, heat is leaving.
* Endothermic. When the thing itself is getting hotter and taking in heat. Like when ice is melting, it takes in heat from around it so the heat makes it go from solid to liquid, or when cooking an egg, for it to cook, you need to take the heat from the pain.
Reactive with oxygen: sodium, potassium, calcium
Unreactive with oxygen: gold
Reactive with water: sodium, potassium
Unreactive with water: copper
Acids: calcium, magnesium
Unreactive with acids: gold, silver, copper