conservation of energy in chemical reactions

energy and chemical reactions

All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. Like the combustion reaction in a furnace, some chemical reactions require less energy to break bonds in reactants than is released when bonds form in products. These reactions, called exothermic reactions, release energy. In other chemical reactions, it takes more energy to break bonds in reactants than is released when bonds form in products. These reactions, called endothermic reactions, absorb energy.

conservation of energy

Whether a chemical reaction absorbs or releases energy, there is no overall change in the amount of energy during the reaction. Thats because energy cannot be created or destroyed. This is the law of conservation of energy. Energy may change form during a chemical reactionfor example, from chemical energy to heat energy when gas burns in a furnacebut the same amount of energy remains after the reaction as before. This is true of all chemical reactions. Q: If energy cant be destroyed during a chemical reaction, what happens to the energy that is absorbed in an endothermic reaction? A: The energy is stored in the bonds of the products as chemical energy. In an endothermic reaction, the products have more stored chemical energy than the reactants. This is represented by the graph on the left in the Figure 1.1. In an exothermic reaction, the opposite is true. The products have less stored chemical energy than the reactants. You can see this in the graph on the right in the Figure 1.1. Note: H represents the change in en- ergy. Q: What happens to the excess energy in the reactants of an exothermic reaction? A: The excess energy is generally released to the surroundings when the reaction occurs. In a home heating system, for example, the energy that is released during combustion in the furnace is used to heat the home.

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questions

which statement about energy and chemical reactions is true?

a) all chemical reactions involve energy.

b) breaking bonds in reactants requires energy.

c) forming bonds in products releases energy.

-->  d) all of the above

energy cannot be created or destroyed in chemical reactions.

-->  a. true

b. false

energy cannot change form during chemical reactions.

a. true

-->  b. false

in an endothermic reaction, products have less chemical energy than reactants.

a. true

-->  b. false

when natural gas burns in a furnace

-->  a) energy is released in the form of heat and light.

b) it takes more energy to break bonds in reactants than to form bonds in products.

c) the natural gas creates energy as it burns.

d) two of the above

diagram questions

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