Which Event Always Involves A Chemical Change? Boiling Melting Conducting Burning

Chapter 1. Essential Ideas

1.3 Concrete and Chemical Properties

Learning Objectives

By the end of this section, you will be able to:

• Identify properties of and changes in matter every bit physical or chemical
• Identify properties of thing every bit extensive or intensive

The characteristics that enable us to distinguish one substance from some other are called backdrop. A physical property is a feature of thing that is not associated with a change in its chemical limerick. Familiar examples of physical properties include density, color, hardness, melting and boiling points, and electric conductivity. Nosotros tin can observe some concrete properties, such as density and color, without irresolute the physical state of the matter observed. Other physical backdrop, such every bit the melting temperature of atomic number 26 or the freezing temperature of water, can but exist observed as matter undergoes a physical change. A physical change is a change in the state or backdrop of matter without any accompanying change in its chemical composition (the identities of the substances contained in the matter). We detect a concrete change when wax melts, when sugar dissolves in coffee, and when steam condenses into liquid h2o (Figure i). Other examples of concrete changes include magnetizing and demagnetizing metals (as is done with common antitheft security tags) and grinding solids into powders (which tin can sometimes yield noticeable changes in color). In each of these examples, at that place is a alter in the physical state, class, or properties of the substance, but no change in its chemical composition.

Effigy one. (a) Wax undergoes a physical change when solid wax is heated and forms liquid wax. (b) Steam condensing within a cooking pot is a physical change, every bit water vapor is changed into liquid water. (credit a: modification of work by "95jb14"/Wikimedia Commons; credit b: modification of work by "mjneuby"/Flickr)

The change of i blazon of matter into another blazon (or the disability to change) is a chemical holding. Examples of chemical backdrop include flammability, toxicity, acidity, reactivity (many types), and heat of combustion. Iron, for instance, combines with oxygen in the presence of water to form rust; chromium does not oxidize (Figure 2). Nitroglycerin is very dangerous because it explodes hands; neon poses almost no hazard considering it is very unreactive.

Figure 2. (a) One of the chemical backdrop of iron is that it rusts; (b) 1 of the chemical properties of chromium is that information technology does not. (credit a: modification of work by Tony Hisgett; credit b: modification of work by "Atoma"/Wikimedia Commons)

To identify a chemical holding, we look for a chemical modify. A chemic change always produces one or more types of affair that differ from the thing sspresent before the modify. The formation of rust is a chemical change because rust is a different kind of matter than the iron, oxygen, and h2o present before the rust formed. The explosion of nitroglycerin is a chemical change because the gases produced are very different kinds of matter from the original substance. Other examples of chemical changes include reactions that are performed in a lab (such equally copper reacting with nitric acid), all forms of combustion (burning), and nutrient existence cooked, digested, or rotting (Figure 3).

Figure three. (a) Copper and nitric acid undergo a chemical modify to course copper nitrate and brown, gaseous nitrogen dioxide. (b) During the combustion of a match, cellulose in the match and oxygen from the air undergo a chemical change to form carbon dioxide and water vapor. (c) Cooking red meat causes a number of chemical changes, including the oxidation of iron in myoglobin that results in the familiar red-to-brown color change. (d) A banana turning chocolate-brown is a chemical change as new, darker (and less tasty) substances form. (credit b: modification of piece of work by Jeff Turner; credit c: modification of work by Gloria Cabada-Leman; credit d: modification of piece of work past Roberto Verzo)

Properties of thing fall into one of ii categories. If the holding depends on the amount of matter present, it is an extensive property. The mass and volume of a substance are examples of extensive properties; for instance, a gallon of milk has a larger mass and volume than a cup of milk. The value of an all-encompassing property is directly proportional to the amount of matter in question. If the property of a sample of matter does not depend on the amount of matter present, it is an intensive belongings. Temperature is an example of an intensive holding. If the gallon and cup of milk are each at 20 °C (room temperature), when they are combined, the temperature remains at 20 °C. As another case, consider the distinct but related properties of heat and temperature. A driblet of hot cooking oil spattered on your arm causes cursory, minor discomfort, whereas a pot of hot oil yields astringent burns. Both the driblet and the pot of oil are at the same temperature (an intensive property), but the pot clearly contains much more than oestrus (extensive belongings).

Hazard Diamond

You may have seen the symbol shown in Figure iv on containers of chemicals in a laboratory or workplace. Sometimes called a "fire diamond" or "hazard diamond," this chemical take a chance diamond provides valuable information that briefly summarizes the various dangers of which to be aware when working with a detail substance.

Figure 4. The National Fire Protection Agency (NFPA) risk diamond summarizes the major hazards of a chemical substance.

The National Burn Protection Agency (NFPA) 704 Adventure Identification System was developed past NFPA to provide safety information well-nigh certain substances. The arrangement details flammability, reactivity, health, and other hazards. Within the overall diamond symbol, the pinnacle (reddish) diamond specifies the level of fire hazard (temperature range for flash bespeak). The blue (left) diamond indicates the level of health hazard. The yellow (right) diamond describes reactivity hazards, such as how readily the substance will undergo detonation or a violent chemical change. The white (bottom) diamond points out special hazards, such every bit if it is an oxidizer (which allows the substance to burn in the absenteeism of air/oxygen), undergoes an unusual or dangerous reaction with water, is corrosive, acidic, alkali metal, a biological chance, radioactive, and then on. Each hazard is rated on a scale from 0 to 4, with 0 beingness no hazard and 4 being extremely hazardous.

While many elements differ dramatically in their chemical and physical backdrop, some elements take similar properties. We can identify sets of elements that exhibit common behaviors. For example, many elements bear rut and electricity well, whereas others are poor conductors. These backdrop tin can be used to sort the elements into three classes: metals (elements that bear well), nonmetals (elements that conduct poorly), and metalloids (elements that have backdrop of both metals and nonmetals).

The periodic table is a tabular array of elements that places elements with like properties close together (Figure 4). You will learn more about the periodic table as you go along your study of chemistry.

Figure 4. The periodic table shows how elements may be grouped according to certain similar backdrop. Note the background colour denotes whether an element is a metallic, metalloid, or nonmetal, whereas the element symbol colour indicates whether it is a solid, liquid, or gas.

Key Concepts and Summary

All substances have distinct concrete and chemical backdrop, and may undergo physical or chemical changes. Physical properties, such as hardness and boiling bespeak, and physical changes, such every bit melting or freezing, exercise not involve a alter in the composition of matter. Chemical backdrop, such flammability and acidity, and chemic changes, such as rusting, involve production of matter that differs from that present beforehand.

Measurable backdrop fall into i of 2 categories. All-encompassing backdrop depend on the amount of affair nowadays, for example, the mass of gold. Intensive properties do not depend on the amount of matter present, for example, the density of gold. Heat is an example of an extensive property, and temperature is an instance of an intensive holding.

Chemistry Cease of Chapter Exercises

1. Allocate the six underlined properties in the following paragraph equally chemic or physical:

   Fluorine is a pale yellow gas that reacts with about substances. The gratuitous element melts at −220 °C and boils at −188 °C. Finely divided metals burn down in fluorine with a bright flame. Nineteen grams of fluorine will react with 1.0 gram of hydrogen.

2. Classify each of the post-obit changes as physical or chemical:

   (a) condensation of steam

   (b) burning of gasoline

   (c) souring of milk

   (d) dissolving of sugar in h2o

   (e) melting of gold

3. Classify each of the following changes as physical or chemical:

   (a) coal burning

   (b) ice melting

   (c) mixing chocolate syrup with milk

   (d) explosion of a firecracker

   (e) magnetizing of a screwdriver

4. The volume of a sample of oxygen gas changed from x mL to 11 mL every bit the temperature changed. Is this a chemical or concrete modify?
5. A 2.0-liter volume of hydrogen gas combined with one.0 liter of oxygen gas to produce two.0 liters of water vapor. Does oxygen undergo a chemic or concrete modify?
6. Explain the difference betwixt extensive properties and intensive properties.
7. Identify the post-obit backdrop as either extensive or intensive.

   (a) volume

   (b) temperature

   (c) humidity

   (d) heat

   (e) boiling point

8. The density (d) of a substance is an intensive property that is defined as the ratio of its mass (m) to its volume (5).

   [latex]\text{density}= \frac{\text{mass}}{\text{volume}}[/latex] [latex]\text{d} = \frac{\text{thousand}}{\text{V}}[/latex]

   Considering that mass and volume are both extensive properties, explain why their ratio, density, is intensive.

Glossary

chemical change

modify producing a different kind of affair from the original kind of matter

chemical property

behavior that is related to the modify of one kind of thing into another kind of thing

all-encompassing property

property of a substance that depends on the corporeality of the substance

intensive property

property of a substance that is independent of the corporeality of the substance

physical change

change in the land or properties of matter that does not involve a change in its chemic composition

physical property

characteristic of affair that is not associated with any change in its chemical limerick

Solutions

Answers for Chemical science End of Chapter Exercises

2. (a) concrete; (b) chemical; (c) chemical; (d) physical; (e) physical

iv. concrete

6. The value of an all-encompassing property depends upon the amount of matter beingness considered, whereas the value of an intensive belongings is the same regardless of the corporeality of affair beingness considered.

eight. Being extensive properties, both mass and book are directly proportional to the corporeality of substance under study. Dividing one extensive belongings by another will in effect "cancel" this dependence on corporeality, yielding a ratio that is independent of amount (an intensive property).

Source: https://opentextbc.ca/chemistry/chapter/physical-and-chemical-properties/

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