* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Energy and Chemical Change Can changes be reversed
Freshwater environmental quality parameters wikipedia , lookup
Marcus theory wikipedia , lookup
Electrochemistry wikipedia , lookup
Process chemistry wikipedia , lookup
California Green Chemistry Initiative wikipedia , lookup
Bioorthogonal chemistry wikipedia , lookup
Drug discovery wikipedia , lookup
Al-Shifa pharmaceutical factory wikipedia , lookup
Chemical reaction wikipedia , lookup
Chemical weapon proliferation wikipedia , lookup
History of chemistry wikipedia , lookup
Chemical weapon wikipedia , lookup
Chemical Corps wikipedia , lookup
Safety data sheet wikipedia , lookup
Chemical plant wikipedia , lookup
Registration, Evaluation, Authorisation and Restriction of Chemicals wikipedia , lookup
Chemical industry wikipedia , lookup
Chemical potential wikipedia , lookup
Physical organic chemistry wikipedia , lookup
Transition state theory wikipedia , lookup
Gas chromatography–mass spectrometry wikipedia , lookup
Stoichiometry wikipedia , lookup
Atomic theory wikipedia , lookup
Energy and Chemical Change Chemical changes involve a change in energy. Think about a fireworks display. The release of thermal energy, light, and sound are signs of chemical changes. All chemical reactions involve energy changes. Chemical reactions can also take in energy. Thermal energy is often needed for a chemical change to take place. To bake bread, for example, you have to put dough in a hot oven. expose Some chemical reactions need energy in the form of light. Plants and some unicellular organisms use the Sun’s energy for photosynthesis. Photosynthesis is the chemical reaction by which these organisms make sugar and oxygen. This process occurs only if the organisms are exposed to light. (verb) to uncover; to make visible Can changes be reversed? ACADEMIC VOCABULARY Think again about a fireworks display. After the fireworks explode, they cannot go back to the chemicals they were before. Chemical changes cannot be reversed. Reading Check change that can be reversed and one that cannot. Key Concept Check 7. Explain how physical and chemical changes affect mass. Conservation of Mass Physical changes do not affect the masses of substances. For example, when an ice cube melts, the mass of liquid water will be the same as the mass of the ice cube. If you cut a sheet of paper into pieces, the total mass of the pieces will be the same as the mass of the paper you started with. Mass is conserved, or unchanged, during a physical change. Mass is also conserved during chemical changes. Antoine Lavoisier, a French chemist, discovered this in the 1700s. The masses of two substances that will chemically react can be measured and added together. After the two substances react to form new substances, the total mass after the reaction can be measured. You will find that the total mass before and the total mass after the reaction are the same. The law of conservation of mass states that the total mass before a chemical reaction is the same as the total mass after the chemical reaction. This is always true because particles are only rearranged. They cannot be created or destroyed, so the total mass cannot increase or decrease. 202 Matter: Properties and Changes Reading Essentials Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 6. Identify one physical Some physical changes cannot be reversed, either. If you cut an apple, it cannot be put back together. Other physical changes can be reversed. For example, if you dissolve salt in a pan of water and then boil the mixture, the water will change to a gas and the salt will be left behind.