Ch10

chemical equation - an equation of chemical formulas that shows the exact numbers of atoms and compounds in a chemical reaction. For example:

A chemical equation is an abbreviated way to show the exact numbers of atoms and compounds in a chemical reaction. Without drawing elaborate diagrams, we can write the baking soda and vinegar reaction as a chemical equation. The arrow shows the direction the reaction goes, from reactants to products.

chemical reaction - a process that rearranges chemical bonds to create new substances.

A chemical reaction is a system of chemical changes that involves the breaking and reforming of chemical bonds to create new substances. A chemical reaction occurs when you mix baking soda with vinegar. The mixture bubbles violently as carbon dioxide gas, a new substance, is formed. The temperature of the mixture also gets noticeably colder. Bubbling, new substances, and temperature change can all be evidence of chemical change (Figure 10.1). UNIT 4 MATTER AND CHANGE

endothermic - A reaction is endothermic if it uses more energy than it releases.

If forming new bonds in the products releases less energy than it took to break the original bonds in the reactants, the reaction is endothermic. Endothermic reactions absorb energy. These reactions need energy to keep going. An example of an important endothermic reaction is photosynthesis. In photosynthesis, plants use energy in sunlight to make glucose and oxygen from carbon dioxide and water

activation energy - energy needed to break chemical bonds in the reactants to start a reaction.

The answer has to do with activation energy. Activation energy is the energy needed to start a reaction and break chemical bonds in the reactants. Without enough activation energy, a reaction will not happen even if it releases energy when it does happen. That is why a flammable material, like gasoline, does not burn without a spark or flame. The spark supplies the activation energy to start the reaction.

nuclear reaction - a process that changes the nucleus of an atom and may turn one element into a completely different element.

forming a precipitate. A precipitate is a solid product that comes out of solution in a chemical reaction. Precipitates usually form many small particles which cause a cloudy appearance in a solution (Figure 10.8).

precipitate - a solid product that comes out of solution in a chemical reaction.

forming a precipitate. A precipitate is a solid product that comes out of solution in a chemical reaction. Precipitates usually form many small particles which cause a cloudy appearance in a solution (Figure 10.8).

exothermic - a reaction is exothermic if it releases more energy than it uses.

is exothermic. Once started, exothermic reactions tend to keep going because each reaction releases enough energy to start the reaction in neighboring molecules. A good example is the burning of hydrogen in oxygen. If we include energy, the balanced reaction looks like this.

products - the new substances which result from a chemical reaction.

with reactants that are combined to make products. The reactants are substances which are combined and changed in the chemical reaction (baking soda and vinegar). The products are the new substances which result from the chemical reaction. The reactants and products may include atoms, compounds, and energy.

reactants - the substances which are combined and changed in the chemical reaction.

with reactants that are combined to make products. The reactants are substances which are combined and changed in the chemical reaction (baking soda and vinegar). The products are the new substances which result from the chemical reaction. The reactants and products may include atoms, compounds, and energy.