exothermic reactions

what is an exothermic reaction

All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. In some chemical reactions, called endothermic reactions, less energy is released when new bonds form in the products than is needed to break bonds in the reactants. The opposite is true of exothermic reactions. In an exothermic reaction, it takes less energy to break bonds in the reactants than is released when new bonds form in the products.

energy change in exothermic reactions

The word exothermic means releasing heat. Energy, often in the form of heat, is released as an exothermic reaction proceeds. This is illustrated in the Figure 1.1. The general equation for an exothermic reaction is: Reactants Products + Energy If the energy produced in an exothermic reaction is released as heat, it results in a rise in temperature. As a result, the products are likely to be warmer than the reactants. Note: H represents the change in en- ergy. Q: You turn on the hot water faucet, and hot water pours out. How does the water get hot? Do you think that an exothermic reaction might be involved? A: A hot water heater increases the temperature of water in most homes. Many hot water heaters burn a fuel such as natural gas. The burning fuel causes the water to get hot because combustion is an exothermic reaction.

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combustion as an exothermic reaction

All combustion reactions are exothermic reactions. During a combustion reaction, a substance burns as it combines with oxygen. When substances burn, they usually give off energy as heat and light. Look at the big bonfire in the Figure 1.2. The combustion of wood is an exothermic reaction that releases a lot of energy as heat and light. You can see the light energy the fire is giving off. If you were standing near the fire, you would also feel its heat.

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questions

in an exothermic reaction, the reactants have more stored chemical energy than the products.

-->  a. true

b. false

in an exothermic reaction, it takes more energy to break bonds in the reactants than is released when new bonds form in the products.

a. true

-->  b. false

all combustion reactions are exothermic reactions.

-->  a. true

b. false

which of the following reactions is exothermic?

a) ch4 + f2  ch3f + hf

b) ch4 + 2o2  co2 + 2h2o

c) 2h2o  2h2 + o2

-->  d) two of the above

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