Changes in Matter

A chemical change occurs when one or more substances change into new substances. A chemical change is also known as a chemical reaction. The appearance of new substances is the sign that a chemical reaction has occurred. In a chemical reaction, the substances present at the start are called reactants. The new substances that are formed in the reaction are called products. A chemical reaction is represented by a chemical equation, which shows the relationship between reactants and products. 

A thin strip of iron with a mass of 15.72 g is placed into a solution containing 21.12 g of copper(II) sulfate and copper begins to form. After a while, the reaction stops because all of the copper(II) sulfate has reacted. The iron strip is found to have a mass of 8.33 g. The mass of copper formed is found to be 8.41 g. What mass of iron(II) sulfate has been formed in the reaction  

In this reaction, there are two reactants and two products, so the law of conservation of mass can be restated as follows. 

Rewrite the equation with the names of the reactants and products. 

To find the mass of iron sulfate, rearrange the equation. 

Real-World Reading Link In a grill, the charcoal is initially a black solid that changes to a glowing red color and eventually ends up as ashes, carbon dioxide, and water. It changes as a result of its physical and chemical properties. 

Phase change As with other physical properties, the state of matter depends on the temperature and pressure of the surroundings. As temperature and pressure change, most substances undergo a change from one state (or phase) to another. A phase change is a transition of matter from one state to another. 

In chemical reactions, the starting substances are called reactants, and the new substances that are formed are called products. Terms such as decompose, explode, rust, oxidize, corrode, tarnish, ferment, burn, or rot generally refer to chemical reactions. 

Mass is conserved in a chemical reaction products have the same mass as reactants. 

Incorporate information from this section into your Foldable. 

You learned in Section 3.1 that scientists can describe matter in terms of physical and chemical properties. For example, a physical property of copper allows it to be drawn into copper wire, and a chemical property of copper accounts for the fact that when a solution of copper ions is combined with ammonia, the copper solution changes to a deep blue color. The key concept in both of these examples is that the substance copper changed in some way. In this section, you ll explore how matter changes as a result of its physical and chemical properties. 

Q Condensation on an icy beverage glass is the result of the phase change of water in a gaseous state to water in a liquid state. 

The characteristic fog of dry ice is actually fine water droplets formed by condensation of water vapor from the air surrounding the very cold dry ice. Refer to Table C-1 in Appendix C for a key to atom color conventions. 

Q The formation of a gas or solid when reactants mix often indicates that a chemical reaction has taken place. Rust is the result of a chemical reaction, o Color changes generally indicate that a chemical reaction has taken place. One example is the color change of tree leaves in the fall. 

Although chemical reactions have been observed over the course of human history, it was only in the late eighteenth century that scientists began to use quantitative tools to monitor chemical changes. The revolutionary quantitative tool developed at this time was the analytical balance, which was capable of measuring very small changes in mass. 

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While Kozma and Russell (2005) recommend the use of visualisation resources, the value of the various formats for various topics is debatable. Kozma and Russell confirm we are not able to say, given the state of the research, for which topics or students it is best to use animations versus still pictures or models (p. 330). Ardac and Akaygun (2005) on the other hand favour the use of dynamic visuals (preferably on an individual basis) over static visuals when presenting molecular representations, confirming that dynamic visuals can be more effective than static visuals in fostering molecular understanding about the changes in matter (p. 1295). Obviously both static and dynamic forms are valuable and can be nsed to complement each other. 

Indeed, the Theosophical infusion of matter with life, and the ability of life force and will to effect the changes in matter demanded by spiritual alchemy and occult chemistry, seemed to find some support from the newly discovered phenomenon of radiation. Besant s On the Watch-Tower column, for instance, noted with excitement an article on the origin of life by Butler Burke published in the Daily Chronicle in 1905. There, Burke noted that radium may be that state of matter that separates, or perhaps unites, the organic and the inorganic worlds, and that radioactivity endows matter with some of the properties of organic matter (quoted in [Besant] 1905a, 481). 

Using the four qualities of matter and four elements as a starting point, Aristotle developed logical explanations to explain numerous natural observations. Both the properties of matter and the changes in matter could be explained using Aristotle s theory. 

DmNiTioir.—>Cheini8atomic composition of bodies, and of those changes in matter which result from an alteration in the relative position of atoms. 

In chemistry, a transformation can be started in some way and will stop when all the possible changes in matter and energy have occurred within the system. The point before which any change in matter or energy has happened is called the initial state, the termination is the final state and the transition between the two is the reaction. The composition of the initial and final states is represented by the chemical reaction equation, which is an expression of the Law of the Conservation of Mass Matter can neither be created nor destroyed. As such the equation should balance electrically as well as chemically, unlike the shorthand biochemical equations seen in many textbooks. 

ANALYZE CHEMICAL AND PHYSICAL PROPERTIES OF AND CHANGES IN MATTER. 

These changes of state appear to be in no way different from allotropic changes in matter in bulk, and it is interesting to see how the break-down or melting of a fairly small detail of the structure, consolidated mainly by the cohesive forces between a few carbon atoms only, may be the cause of such allotropic changes. 

Suppose that you are a consultant to the National Science Foundation. In a proposal for a 10 million grant, a claim is made that a method will be developed to make a machine that produces twice as much energy as it uses up, with no permanent changes in matter. Would you recommend that government money be spent on this proposed research Explain your reasoning. 

Explain that physical and chemical changes in matter involve transfers of energy. 

Apply the law of conservation of energy to analyze changes in matter. Distinguish between heat and temperature. 

Every Change in Matter Involves a Change in Energy... 

Any change in matter in which energy is absorbed is known as an endothermic process. The melting of ice and the boiling of water are two examples of physical changes that are endothermic processes. 

Changes in matter can be chemical or physical. However, only chemical changes produce new substances. 

Every change in matter involves a change in energy. 

The differing properties of matter are due to the size, shape, and movement of atoms. Apparent changes in matter result from changes in the groupings of atoms and not from changes in the atoms themselves. 

The flash, bang, sparks, and powder all occur because of events that take place among atoms of sodium and chlorine. Every change in matter is caused by something happening between atoms, molecules, or ions. In other words, every macroscopic change in matter has a submicroscopic explanation. One of your tasks as a chemistry student is to observe reactions and learn how to explain them on the submicroscopic scale. 

What causes these changes to occur In this chapter, you will learn some of the factors that determine whether a change will occur and how fast it will go if it does occur. You will also review how observing macroscopic changes in matter can indicate whether or not a chemical change has occurred. You will then use what you have learned about chemical formulas to represent chemical changes using equations. 

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