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May 22nd, 2017
Exothermic and Endothermic Reactions

During unit 9, we had learned about exothermic and endothermic reactions. These reactions have one thing in common which is, both reactions are involved in the transfer of heat. Although, their methods of transferring heat are different. Exothermic reaction is when heat is released in other words it is the transfer of energy to the surroundings. While an Endothermic reaction is when heat is absorbed in other words, Endothermic reactions take in energy from surroundings. An easier way to remember and distinguish between these two types of reaction is remembering the meaning for the prefixes. For example for exothermic, the prefix exo-, means external or outside. While the prefix of endothermic is endo-, which means internal or inside.

Two examples of endothermic reactions include photosynthesis and cooking an egg. During photosynthesis plants absorb heat energy (heat energy ENTERS the plant) from sunlight to convert carbon dioxide and water into glucose and oxygen. As for cooking an egg, during the process heat energy is absorbed from the pan to the cook egg (energy ENTERS the cook egg). As for the two examples of exothermic reactions include combustion and rain. During combustion, while burning carbon-containing compounds which uses oxygen from air, carbon dioxide, water and lots of heat are produced and RELEASED to the surroundings. As for rain, during the condensation of water vapor into rain releases energy (into the surroundings) in the form of heat .

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/chemreac/energychangesrev1.shtml
https://www.khanacademy.org/test-prep/mcat/chemical-processes/thermochemistry/a/endothermic-vs-exothermic-reactions
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Unit 9: pH levels/Logarithmic scale

pH levels are the measurement of acidity or base of the liquid in question. The scale goes up to the number 14. On the scale, below a seven on the ph scale means that the liquid is considered an acid. Above a seven on the ph scale means that the liquid is considered base. Seven on itself without decimals, however, are not acid nor base, they are neutral, for example water. Ph is measured by the amount of hydrogen ion+ there are in the substance. Ph is not measured by a linear scale but a logarithmic scale. Which means that between number there is a values times 10 bigger rather than the normal 1. The value between each ph number is huge, unlike normal linear. An example of the values for logarithmic scale is: the difference between 2 numbers on the scale is 10x, three is 100x, four is 1000x, and so on
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May 22nd, 2017
The pH Scales, Acids, Bases

In Unit 9, the term pH is one of the most important key concept since it is used quite often throughout the unit. pH refers to a measure of hydrogen ion concentration of a solution. Solutions with a high concentration of a hydrogen ions have a low pHs, while solutions with a low concentration of a hydrogen ions have a high pHs. The pHs scale is a measure of acidity or alkalinity (basic) of water soluble substances. The pH range or value is a number from 0 to 14, with 7 as the neutral point. Numbers above 7 indicates alkalinity (basic) which increases as the number increases while, numbers below 7 indicates acidity which increases as the number decreases. Although this scale is not a linear scale (centimeter or inch scale, in which the two adjacent values have the same difference) as it is a logarithmic scale. A logarithmic scale is a scale in which two adjacent values increase or decrease by a factor of 10. For example a pH of 3 is 10 times more acidic than a pH of 4, and 100 times more acidic than a pH of 5. Similar to the pH of 9 is 10 times more alkaline than a pH of 8. The scale is divided in half, one side is 0-7 which is on the left side and measures the acidic substances. While the right side is 7-14 which measures the alkaline or basic substances. Examples of acidic substances include Hydrochloric Acid, Vinegar, Lemon and battery acid. As for alkaline substances which include bleach and drain cleaner. A substance with a pH which is near to 7 tends to be weaker but, a substance with a pH of 7 would be neutral which includes pure water.

Acids and bases have different distinct features including its taste, how it feels and many more. For example acids taste sour while bases taste bitter, acids don't feel slippery while bases feel slippery. Acids release hydrogen (H^+) ions in aqueous solutions while, bases release hydroxide (OH^-) ions in aqueous solutions. An aqueous solution is a solution in which the solvent is water. Acids damage metals while bases don't. Acids react with metals to produce a compound and hydrogen gas while, bases do not react with metals. The pH levels are measured using the litmus papers. For acids the litmus paper will turn red or pink while the bases will turn blue.

https://www.slideshare.net/OhMiss/acids-bases-7096291
http://chemistry.elmhurst.edu/vchembook/184ph.html
http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/chemical_synthesis/acidsalkalisrev2.shtml
http://www.businessdictionary.com/definition/pH-scale.html
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Endothermic and Exothermic Reaction

Exothermic reactions transfer energy to the surroundings. Endothermic reactions take in energy from the surroundings. Exothermic reactions are reactions that transfer energy to the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter. Examples of an exothermic reaction are burning, neutralisation reactions between acids and alkalis and the reaction between water and calcium oxide

Endothermic reactions are the reactions that that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder. Examples of endothermic reactions are melting ice cubes, melting solid salts and evaporating liquid water.


Source:
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/chemreac/energychangesrev1.shtml
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pH scales

pH scales is a measure to how acid or basic a substance is. The pH scale ranges from 0-14. 0 being the most acidic, and 14 being the most basic. In the middle, 7, is considered neutral. The pH scale is logarithmic and as a result, each pH value that is below 7 is 10 times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5, and pH 4 would be 100 times more acidic than pH 6. Pure water is neutral, which has a pH level of 7.
An acid is a substance that donates hydrogen ions, and a base is a substance that accepts hydrogen ions.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/chemical_synthesis/acidsalkalisrev2.shtml


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Acid - Base

Solutions are classified as acidic or basic based on their hydrogen ion concentration relative to pure water. If a liquid is acidic it means that the liquid has a high concentration of hydrogen ions (H+) greater than that of pure water. If a liquid is basic it means that has a low (H+) concentration, less than that of pure water.
The concentration of hydrogen ion in a solution are typically measured by pH. PH translates the values of the concentration of the hydrogen ion into numbers between 0 and 14. In pure water, which is neutral, the concentration of the hydrogen ion is 10−7 gram-equivalents per litre, which corresponds to pH of 7. A solution with a pH less than 7 is considered acidic; a solution with a pH greater than 7 is considered basic.



Source:

https://www.khanacademy.org/science/biology/water-acids-and-bases/acids-bases-and-ph/a/acids-bases-ph-and-bufffers

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Exothermic and Endothermic Reactions

Exothermic and endothermic reactions occur during the phase changes. There are the movements of heat during phase changes. An exothermic reaction takes place when the heat is releasing from the system into the environment while an endothermic reaction takes place when the heat is moving from the environment into the system. In both of these reactions, they both have the word “thermic”, which means heat. The easy way to remember these reaction is to look at the prefixes. Because the word “exo” in exothermic means outside or outer, we can know that the movement of the heat in this reaction should move out of the system. However, the word “endo” in endothermic means within so we can know that the movement of the heat in this reaction should move from the environment into the system. In phase change, an exothermic reaction would occur when cooling down water while an endothermic reaction would occur when boiling the water.

Sources: https://chem.libretexts.org/Textbook_Maps/Introductory_Chemistry_Textbook_Maps/Map%3A_Introductory_Chemistry_(CK-12)/17%3A_Thermochemistry/17.10%3A_Heats_of_Fusion_and_Solidification
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pH scale

A pH scale is a scale that measure the acidity and alkalinity of a substance. The scale ranges from 0-14. A pH less than 7 is acidic while a pH more than 7 is basic and a pH of 7 is neutral. Because of this, if the substance has a pH of 0, it is very acidic but it is very basic when having a pH of 14. There are some different properties between acidic substance and basic substance. One difference between acidic substance and basic substance is the taste. Acidic substance mostly taste sour while basic substance taste bitter. Even though we can identify whether if the substance is acidic and basic by the taste, you should not taste substance in the lab since they are dangerous. An example of an acidic substance is lemon which has a pH about 2 while the basic substance would be baking soda which normally has a pH of 9. A pH is very important to our lives since it can be used to show the alkalinity of a product like soap to show that we should use it or not.

Sources:
http://www.chemistryland.com/CHM130FieldLab/Lab12/Lab12.html

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Acids and Bases

Every liquids are either acidic or basic. The pH scale is one of the factors that identify acids and bases. Acids have pH of 0-7 and bases have pH of 7-14. Although the pH scale can recognize which is acid and which is base, there are some properties that can help differentiate the two. First off, the taste. Acids have a sour taste while bases have a bitter taste. Vinegar and lemon are considered as acids, soap and ammonia as bases. Bases also have a slippery feel to it so soaps are slippery. Both acids and bases can conduct electricity when dissolved in water so they are electrolytes. When dissolved in water, all acids produce Hydrogen ions (H+) and they produce Hydrogen gas when react with metals. As for bases, they produce Hydrogen oxide ions (OH-)

http://www.chem4kids.com/files/react_acidbase.html

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Unit 9: Rates of Reactions (Collision Theory)

What are the rates of chemical reactions and how do you speed them up? The rate of reactions is how long it takes to have a chemical reaction. Different reactions occur at different rates, which is expected because when you mix a mixture not ALL atoms in that mixture will just instantaneously react. Even the same substance reacts with different times under certain conditions. But how could you speed up a reaction? There are 4 total ways to speed up a reaction using collision theory. First, increase the concentration of the liquid. The more atoms, the bigger chance of collision. Second, decrease the surface area to make more collision in the atoms, shrinking the size of the container of the liquids, this concentrates the liquid. Third, increase the temperature of the liquid. Atoms move much faster when the temperature increases, by making the atoms move faster, this increase the chances for two or more atoms hitting each other. Fourth, use a chemical catalyst. The chemical catalyst is like a bonding help because it lowers activation energy in the liquid, making chemical rects require less energy to happen.
wikipedia.com
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