Endothermic+&+Exothermic+Reactions

=Exothermic Reactions =

The two types of main chemical reactions are endothermic and exothermic. These two chemical reactions are completely different from each other, but both can be either harmful or harmless. Endothermic reactions absorb energy and exothermic reactions release energy. So they're complete opposites.

Reactions that release energy and give off heat are called exothermic reactions. If the total amount of energy of the reaction products is less than the total amount of heat of the reactants, the reaction has to be exothermic. However, in some chemical reactions, there is a net transfer of energy from the reactants to their surroundings. == The heat of reaction is one of the two factors that makes exothermic reactions spontaneous. The heat of reaction is the heat that is released or absorbed by chemical reactions. It is usually represented by a negative ΔH if it’s an exothermic reaction. This process depends on the breaking or making of chemical bonds. For example, in the making of chemical bonds heat is released. Therefore, making it and exothermic reaction.

Another one of the two factors that makes exothermic reactions spontaneous is randomness. Some reactions are distinguished by an increase in randomness. The particles that are involved in the reaction becoming more spread out is one example. An increase in randomness is a factor favoring the spontaneous change. Even a spontaneous reaction may not happen fast. It might even need an initial boost of energy to get started. This energy boost is called the activation energy.



There are many examples of exothermic reactions. Since and exothermic reaction is one that releases heat, there are many examples. Some of these examples of exothermic reactions are the burning of fuels, the dissolving of concentrated sulfuric acid in water, and the combination of hydrogen and oxygen to form water. = = =Endothermic Reactions = When the total amount of energy is more then the total amount of heat, an endothermic reaction has occurred. The heat of reaction, which is the heat released or absorbed by a chemical reaction, all depends on the chemical bonds. When the chemical bonds are being broken down, it’s an endothermic reaction. Which is what makes the heat become absorbed.

Since endothermic reactions contain a net of absorption, they can be spontaneous. Usually exothermic reactions happen more spontaneously then endothermic, but it can still happen. This they occur without continued energy input. One way you can tell if it’s spontaneous is by it’s randomness. If the reaction is spread out it is developing spontaneous change. If this change increases enough in randomness, it can outweigh the maximize amount of heat needed by an endothermic reaction. Even though this reaction can happen spontaneously, it doesn’t necessarily mean that it happens fast. Endothermic reactions are represented by a positive ΔH in the heat of reactions.

Endothermic reactions require an input of energy in the form of heat for it to proceed. You know that this is happening when the reactants feel cold and the temperature of the reactants decreases. Photosynthesis needs energy absorbed from the sun as a form of energy. Reactions like this need to break the chemical bonds in the reactants so it can be absorbed and once this has happened, bonds are formed as products. Photosynthesis produces products with bonds that have more energy then the reactants’ bonds.

Energy changes are determined by immediately measuring the heat released or absorbed in a reaction. Hess’s Law helps calculate the amount of steps in the heat of reaction, and can also be calculated by using this law. This law states that “the heat evolved or absorbed in a chemical process is the same whether the process takes place in one or in several steps.” So this law helps see how much heat is absorbed in an endothermic reaction.

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=__ Resources __ =

**Amanda:** "Chemical Energy." Expert Space. Web. 30 Jan. 2012. . <span style="font-family: Georgia,serif;">"Energy Transfer." Expert Space. Web. 30 Jan. 2012. <http://tinyurl.com/884a536>. <span style="font-family: Georgia,serif;">"Endothermic Reactions and Exothermic Reactions." Expert Spaces. Web. 30 Jan. 2012. <http://tinyurl.com/7haoyyg>. <span style="font-family: Georgia,serif;">"Hess's Law." Expert Spaces. Web. 30 Jan. 2012. <http://tinyurl.com/7vfz74q>. <span style="font-family: Georgia,serif;">"Chemical Energy and Hess's law." Hess's Law. Web. 30 Jan. 2012. <http://tinyurl.com/3qtt6oq>.

<span style="font-family: Georgia,serif; font-size: 120%;">**Lauren:**

<span style="font-family: Georgia,serif;">"Chemical Reactions." The New Book of Knowledge. Grolier Online, 2012. Web. 25 Jan. 2012. <span style="font-family: Georgia,serif;">Exothermic and Endothermic Reactions. Prod. Brian Jerome. Brian Jerome, 1998. Discovery Education. Web. 25 January 2012. <http://www.discoveryeducation.com/>. <span style="font-family: Georgia,serif;">"Chemical Energy." Chemical Reactions. Expert Space, 2012. Web. 30 Jan. 2012.