Chemical Change Definition in Chemistry

Chemical Change Definition in Chemistry A chemical change, also known as a chemical reaction, is a process where one or more substances are altered into one or more new and different substances. In other words, a chemical change is a chemical reaction involving the rearrangement of atoms. While a physical change can often be reversed, a chemically change typically cannot be, except through more chemical reactions. When a chemical change occurs, there is also a change in the energy of the system. A chemical change that gives off heat is called an exothermic reaction. One that absorbs heat is called an endothermic reaction. Key Takeaways: Chemical Change A chemical change occurs when one substance is transformed into one or more new products via a chemical reaction.In a chemical change, the number and type of atoms remains constant, but their arrangement is altered.Most chemical changes are not reversible, except via another chemical reaction. Examples of Chemical Changes Any chemical reaction is an example of a chemical change. Examples include: Combining baking soda and vinegar (which bubbles off carbon dioxide gas)Combining any acid with any baseCooking an eggBurning a candleRusting ironAdding heat to hydrogen and oxygen (produces water)Digesting foodPouring peroxide on a wound In comparison, any change that does not form new products is a physical change rather than a chemical change. Examples include breaking a glass, cracking open an egg, and mixing sand and water. How to Recognize a Chemical Change Chemical changes may be identified by: Temperature Change - Because there is an energy change in a chemical reaction, there is often a measurable temperature change.Light - Some chemical reactions produce light.Bubbles - Some chemical changes produce gases, which can be seen as bubbles in a liquid solution.Precipitate Formation - Some chemical reactions produce solid particles that may remain suspended in a solution or fall out as a precipitate.Color Change - A color change is a good indicator that a chemical reaction has occurred. Reactions involving transition metals are particularly likely to produce colors.Odor Change - A reaction may release a volatile chemical that produces a characteristic scent.Irreversible - Chemical changes are often difficult or impossible to reverse.Change in Composition - When combustion occurs, for example, ash may be produced. When food rots, its appearance visible changes. Note a chemical change may occur without any of these indicators being observed. For example, the rusting of iron produces heat and a color change, but it takes a long time for the change to be evident, even though the process is ongoing. Types of Chemical Changes Chemists recognize three categories of chemical changes: inorganic chemical changes, organic chemical changes, and biochemical change. Inorganic chemical changes are chemical reactions that dont generally involve the element carbon. Examples of inorganic changes including mixing acids and bases, oxidation (including combustion), and redox reactions. Organic chemical changes are those the involve organic compounds (containing carbon and hydrogen). Examples include crude oil cracking, polymerization, methylation, and halogenation. Biochemical changes are organic chemical changes that occur in living organisms. These reactions are controlled by enzymes and hormones. Examples of biochemical changes include fermentation, the Krebs cycle, nitrogen fixation, photosynthesis, and digestion.

Definition and Examples of Aspect in English Grammar

Definition and Examples of Aspect in English Grammar In English grammar, aspect is a verb form (or category) that indicates time-related characteristics, such as the completion, duration, or repetition of an action. (Compare and contrast with tense.) When used as an adjective, its  aspectual. The word comes from Latin, meaning how [something] looks The two primary aspects in English are the perfect (sometimes called perfective) and the progressive (also known as the continuous form). As illustrated below, these two aspects may be combined to form the perfect progressive. In English, aspect is expressed by means of particles, separate verbs, and verb phrases. Examples and Observations Perfect AspectThe perfect aspect describes events occurring in the past but linked to a later time, usually the present. The perfect aspect is formed with has, have, or had the past participle. It occurs in two forms:​ Perfect Aspect, Present Tense:History has remembered the kings and warriors, because they destroyed; art has remembered the people, because they created.(William Morris, The Water of the Wondrous Isles, 1897)​ Perfect Aspect, Past Tense:At fifteen life had taught me undeniably that surrender, in its place, was as honorable as resistance, especially if one had no choice. (Maya Angelou, I Know Why the Caged Bird Sings, 1969) Progressive AspectThe progressive aspect usually describes an event that takes place during a limited time period. The progressive aspect is made up of a form of be the -ing form of the main verb.​ Progressive Aspect, Present Tense:Shes loyal and is trying to wear her thin flippy hair in cornrows.(Carolyn Ferrell, Proper Library, 1994) Progressive Aspect, Past Tense:I was reading the dictionary. I thought it was a poem about everything. (Steven Wright) The Difference Between Tense and AspectTraditionally . . . both aspects [perfect and progressive] are treated as part of the tense system in English, and mention is made of tenses such as the present progressive (e.g. We are waiting), the present perfect progressive (e.g. We have been waiting), and the past perfect progressive (e.g. We had been waiting), with the latter two combining two aspects. There is a distinction to be made, however, between tense and aspect. Tense is concerned with how time is encoded in the grammar of English, and is often based on morphological form (e.g. write, writes, wrote); aspect is concerned with the unfolding of a situation, and in English is a matter of syntax, using the verb be to form the progressive, and the verb have to form the perfect. For this reason combinations like those above are nowadays referred to as constructions (e.g. the progressive construction, the present perfect progressive construction). (Bas Aarts, Sylvia Chalker, and Edmund Weiner, Oxford Dictionary of English Grammar, 2nd ed. Oxford University Press, 2014) present perfect progressive: God knows how long Ive been doing it. Have I been talking out loud? past perfect progressive: He had been keeping it in a safety deposit box at the Bank of America. For months she had been waiting for that particular corner location. Present Perfect Progressive and Past Perfect ProgressiveThe perfect aspect most often describes events or states taking place during a preceding time. The progressive aspect describes an event or state of affairs in progress or continuing. Perfect and progressive aspect can be combined with either present or past tense...Verb phrases can be marked for both aspects (perfect and progressive) at the same time: The perfect progressive aspect is rare, occurring usually in the past tense in fiction. It combines the meaning of the perfect and the progressive, referring to a past situation or activity that was in progress for a period of time. (Douglas Biber, Susan Conrad, and Geoffrey Leech, Longman Student Grammar of Spoken and Written English. Longman, 2002)