Physical and Chemical Changes

9 Key excerpts on "Physical and Chemical Changes"

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  eBook - ePub

  200 Science Investigations for Young Students

  Practical Activities for Science 5 - 11

  • Martin Wenham(Author)
  • 2000(Publication Date)
  • SAGE Publications Ltd

    (Publisher)

  These are changes which alter the physical properties and often the appearance of materials, while the actual substances involved remain the same. However fundamentally a material seems to alter when it undergoes physical changes, the kind of material it is does not change at all. Changes which do involve making new kinds of material are chemical changes (Section 9.1). It is important to avoid any confusion between the concepts of physical and chemical change on the one hand, and reversible and non-reversible change on the other. These pairs of ideas are quite independent of each other. There are physical changes which are reversible (e.g. melting ice or dissolving sugar in water) and others which are non-reversible (e.g. cracking and beating an egg or grinding grain to flour); and similarly with chemical changes. Because physical changes are very varied and often encountered in everyday life, it is useful to think of them as falling into broad groups, depending on their causes. Changes of state brought about by the transfer of thermal energy are investigated in Sections 6.2 and 6.3 ; those caused by applying forces to objects and materials in Chapter 7 ; while those brought about by mixing and separation are investigated in the remainder of this chapter. Mixtures A mixture is made when two or more materials are physically combined or mixed together while remaining chemically distinct. To understand mixtures and their properties it is necessary not only to mix materials and observe the changes this brings about, but also to use and if necessary devise the means of separating them again

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  Introductory Chemistry

  An Active Learning Approach

  • Mark Cracolice, Edward Peters, Mark Cracolice(Authors)
  • 2020(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Chemical property: The chemical changes possible for a substance. Goal 5 Distinguish between Physical and Chemical Changes at both the particulate level and the macroscopic level. Physical change: Alteration in physical form without change in identity. Chemical change: Identity of original substance changed to something new. Goal 6 Distinguish between a pure substance and a mixture at both the par- ticulate level and the macroscopic level. Pure substance: One chemical with distinct set of physical and chemical properties; cannot be separated by physical changes. Mixture: Two or more pure substances; properties vary, depending on relative amounts of pure substances; components can be separated by physical changes. Goal 7 Distinguish between homoge- neous and heterogeneous matter. Homogeneous: Same appearance, composition, properties throughout. Solution: A homog- enous mixture. Heterogeneous: Different phases visible, variable properties in different parts of sample. Goal 8 Describe how distillation and filtra- tion rely on physical changes and proper- ties to separate components of mixtures. Separations are usually based on different physical properties of components. Distillation separates based on volatilities of components. Filtration separates based on particle size. A porous medium is used to separate mixture components based on size (a physical property). Goal 9 Distinguish between elements and compounds. Element: Pure substance, cannot be decomposed chemically into other pure substances. Compound: Pure substance that can be decomposed chemically into other pure substances. Goal 10 Distinguish between elemental symbols and the formulas of chemical compounds. Elemental symbol: Capital letter, sometimes followed by small letter. Formula of compound: Elemental symbols of elements in compound. Subscripts show number of atoms of each element. Goal 11 Distinguish between atoms and molecules.

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  Foundations of College Chemistry

  • Morris Hein, Susan Arena, Cary Willard(Authors)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  Matter can undergo two types of changes, physical and chemical. Physical changes are changes in physical properties (such as size, shape, and density) or changes in the state of matter without an accompanying change in composition. The changing of ice into water and water into steam are physical changes from one state of matter into another. No new substances are formed in these physical changes. When a clean platinum wire is heated in a burner flame, the appearance of the plati- num changes from silvery metallic to glowing red. This change is physical because the platinum can be restored to its original metallic appearance by cooling and, more impor- tantly, because the composition of the platinum is not changed by heating and cooling. In a chemical change, new substances are formed that have different properties and composition from the original material. The new substances need not resemble the original material in any way. When a clean copper wire is heated in a burner flame, the appearance of the cop- per changes from coppery metallic to glowing red. Unlike the platinum wire, the copper wire is not restored to its original appearance by cooling but instead becomes a black material. This black material is a new substance called copper(II) oxide. It was formed EXAMPLE 4.1 You have three flasks that contain chlorine gas, nitrogen dioxide gas, and oxygen gas. Describe how you would use physical properties to identify the contents in each flask. SOLUTION Use Table 4.1 to compare the compounds and note their colors. You will find that chlorine is a greenish yellow color, nitrogen dioxide is reddish brown, and oxygen is colorless. Now you have the information to identify the contents in each flask. P R A C T I C E 4 . 1 You are given three samples of silver compounds: AgCl, AgBr, and AgI. Arrange these silver compounds in the order of their percent silver by mass (highest to lowest).

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  Physical Science NQF2 SB

  TVET FIRST

  • L Greenstein M Keane(Author)
  • 2013(Publication Date)
  • Macmillan

    (Publisher)

  140 Topic 6, Module 16 Module 16 Physical and Chemical Changes Module outcomes When you have completed this module, you will be able to… ! identify, define and distinguish between Physical and Chemical Changes and give examples ! identify and apply physical and chemical methods of separating mixtures (solids, liquids and gases) ! identify and describe electrolytes ! describe hydrolysed salts as sources of electrolytes and determine the solubility of salts as measured by conductivity of the solution ! identify acids as potential sources of electrolytes ! identify the interaction (displacement reactions) and effect of ions in aqueous solution (e.g. corrosive) ! calculate atomic, molecular and formula mass ! calculate the amount of substance in mole and gram ! calculate the concentration of solutions. Words & Terms Solvent: substance in which another substance (the solute) is dissolved Solute: substance that is suspended in a solution Assessment Activity 16.1 Physical and Chemical Changes We can change matter in different ways. We can mix it together, freeze it, melt it, boil it or get it to react with different kinds of matter. Some kinds of changes are reversible – in other words, it is easy to get the matter back to the same state it was in before the change. Other kinds of changes are irreversible – it is very difficult or impossible to get the original materials back from the new product. One example of a physical change is dissolving one substance in another. For example, when you mix a concentrated drink powder in water, the drink powder is the solute and the water is the solvent. The particles of the solute and the solvent mix together to form a homogeneous liquid called a solution. The more solute (e.g. drink powder) that is in the solution, the more concentrated it is. The more solvent that is in the solution, the more dilute it is. (See Unit 16.4 for more about the concentration of solutions.) Some substances do not dissolve.

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  Basics for Chemistry

  • David A. Ucko(Author)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  Once mixed, the iron and PHYSICAL CHANGE sulfur can be physically separated. For example, as shown in Figure 9-1(a), iron can be removed from the mixture with a magnet, leaving only the sulfur behind. In a mixture, the properties of each substance remain the same; iron still acts like iron, and sulfur still acts like sulfur. However, if we mix iron with sulfur and then heat the mixture, a chemical change takes place. A new substance forms that has different properties from either iron or sulfur. The magnet no longer can separate the iron and sulfur (Figure 9-1(b)). Chemical bonds have formed be-tween the atoms of these two elements. A single new substance is now present instead of two. This new substance is a compound, iron(II) sulfide. Chemical changes generally result in physical changes as well. Phys-ical changes involve changes in the state, color, odor, density, and other characteristics of a substance. The occurence of physical change in a substance, however, does not guarantee that a chemical change has taken place. For example, if we boil water, we see a physical change—the liquid bubbles and steam forms. However, the chemical composition and identity of the water remains the same, and no chem-ical change takes place. A chemical reaction, the process of chemical change, is caused by the making or breaking of chemical bonds. Reactions occur when atoms or molecules bump into each other in just the right way, and also with enough energy to cause existing chemical bonds to break or new bonds to form. During a chemical reaction, atoms rearrange themselves into new combinations. You are already familiar with some chemical re-actions. The rusting of iron, the burning of wood, and the digesting of food all involve chemical change. All compounds are formed by chemical reactions. The same com-pound can be formed by several different chemical reactions. But re-gardless of how a particular compound is made, its composition is always the same.

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  Janice VanCleave's Big Book of Science Experiments

  • Janice VanCleave(Author)
  • 2020(Publication Date)
  • Jossey-Bass

    (Publisher)

  Part I 1 CHEMISTRY C hemistry is the study of matter, its physical and chemical properties, and how it changes. This science involves all of one’s senses: seeing, hearing, tasting, feeling, and smelling. It is listed first in this book because chemistry concepts are a springboard into the other sciences. You cannot understand the physics concept of electricity without understanding the chemistry of atoms, or the formation of crystals in caves in earth science, or biochemical reactions in the fruit ripening process in biology without understanding chemical reactions. Chemistry is not restricted to scientists working in laboratories; instead, knowledge of chemistry is important in our everyday lives. Who knows? You might be on some reality show or confronted with an unexpected survival situation. You would be cut off from electrical devices. Chemistry knowledge would help you use available resources. Yes, your brain is your best survival tool in emergencies; but it is also the best problem-solving tool you have. Chemistry is all about problem solving, and the investigations in this book contain the foundation on which to build and sharpen your chemistry knowledge. 2 Matter Matter is anything that occupies space and has mass (an amount of matter making up a material). Matter is the stuff that makes up the Universe. Figure 1 shows a flow chart for the different types of matter. The term pure substance refers to one kind of matter, such as an element or a compound; without the adjective “pure,” the term substance is commonly used to refer to any material pure or not, and that is how it is used in this book. Mixture is a term that refers to the combination of different substances. Elements At this time, 118 different elements have been identified. The 94 elements that occur in nature are called natural elements, examples being carbon, oxygen, nitrogen, and sulfur. Synthetic elements are the 24 elements made by scientists in a laboratory.

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  Physical Sciences

  Curriculum Resources and Activities for School Librarians and Teachers

  • Amy Bain, Janet Richer, Janet Weckman(Authors)
  • 2001(Publication Date)
  • Libraries Unlimited

    (Publisher)

  28. Explain that mixtures can be made up of two or more compounds (Chapter 2). 29. Explain that mixtures can be made up of several different elements and compounds (Chapter 2). 30. Explain that a mixture equals two or more materials that, when combined, each retains its origi- nal properties (Chapter 2). 31. Explain that mixtures can be solutions (Chapter 2). 32. Explain that a solution is one substance that is dissolved into another substance (Chapter 2). 33. Cite the common compound when given its formula, and vice versa (Chapter 1). 34. Describe a radioactive element (Chapters 1, 2). 35. Explain physical and chemical properties, differentiate between them, and cite examples of each (Chapters 1, 2). 36. Recognize that energy is required to change matter from one state to another (Chapter 2). 37. Explain the difference between nuclear fusion and nuclear fission (Chapter 2). 38. Explain chemical bonding (Chapter 2). 39. Differentiate between chemical and physical changes in matter (Chapter 2). 40. Define the law of conservation of matter (Chapter 2). 41. Name the four basic types of chemical reactions, citing examples of each (syntheses, single re- placement, decomposition, double replacement) (Chapter 2). 42. Explain oxidation/valence and demonstrate how to determine it for common elements (Chap- ter 2). 43. Compare and contrast a chemical change and a physical change (Chapter 2). 44. Understand that a chemical change results in a change in chemical properties (Chapter 2). This page intentionally left blank Chapter 1 Mass and Measurement Teaching Resources Books containing experiment(s) relating to the subject matter are marked with a plus sign (+) before and after the title. P Capacity, by Henry Pluckrose (Franklin Watts, 1995) Full-page photographs and brief text describe capacity and how we measure it, connecting it to mathematics.

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  Hazardous Substances

  Risks and Regulations

  • Thomas Schupp(Author)
  • 2020(Publication Date)
  • De Gruyter

    (Publisher)

  2  Physical and chemical properties of substances

  Understanding physical and chemical properties of substances is a prerequisite for proper understanding of not only physical–chemical hazards, but also for the understanding of substance behavior in the environment and in organisms.

  Environmental behavior covers the emission, distribution and fate of a substance in the environment, and this perspective shows similarities to the adsorption, distribution, metabolism and excretion (ADME) of a substance in an organism as discussed in Chapter 3, if an ecosystem (or nature) is regarded as an organism.

  Physical–chemical properties of substances are part of their identification, and in the field of hazardous substances and risk assessment, proper identification and characterization is crucial for the success of toxicological and environmental investigations. This chapter starts with the identification of substances.

  2.1  Identification of substances

  Identification of a substance starts with simple physical properties that can be checked quickly and without sophisticated equipment. For solids, it is the melting point and visual appearance; for liquids, it is the refraction index, perhaps extended to boiling point, viscosity and density. These methods may provide a hint on purity, already, and it may occur that some limited data on identification are sufficient to check the specification of a product agreed upon between supplier and customer. Nevertheless, a more in-depth check on purity or identification of impurities can be very important. Just as one example: the substance aniline was the parent for the name “aniline-cancer,” describing bladder cancer that was comparatively frequently detectable in workforces in aniline production plants. Later, it turned out that impurities in the technical aniline – namely benzidine and 2-naphthylamine – were the causative agents. To detect and quantify such by-products and impurities, spectrometric and chromatographic methods are required. The European chemicals regulation actually requires the full characterization of a “mono-constituent” substance (see Chapter 8) submitted for registration by UV, IR, NMR and MS spectra, as far as appropriate, and to make use of chromatographic methods [gas chromatography (GC), high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC)] to identify every component that contributes to at least 0.1% to the technical substance. Lower detection limits may be required if the presence of specific critical impurities cannot be excluded.

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  Hands-On Science and Technology for Ontario, Grade 5

  An Inquiry Approach

  • Jennifer E. Lawson, Jennifer Lawson(Authors)
  • 2020(Publication Date)
  • Portage & Main Press

    (Publisher)

  ■ ■ If you heat liquid water, then . ■ ■ If you remove heat from steam, then . ■ ■ If you remove heat from liquid water, then . Define these terms: ■ ■ Freezing: ■ ■ Melting: ■ ■ Evaporation: ■ ■ Condensation: 3.6.2 Portage & Main Press, 2018 · Hands-On Science and Technology for Ontario · Hands-On Science and Technology for Ontario, Grade 5 · ISBN: 978-1-55379-711-1 Learning Centre EX How Important Is Precipitation to Life on Earth? 1. Read the books about precipitation and the water cycle. ■ ■ Think about how precipitation affects life on Earth. ■ ■ Think about what would happen on Earth if there was no precipitation. 2. Make a concept map on a large sheet of paper. 3. Use words and pictures to record your ideas. 3.6.2 Properties of and Changes in Matter s 233 Portage & Main Press, 2018 · Hands-On Science and Technology for Ontario · Hands-On Science and Technology for Ontario, Grade 5 · ISBN: 978-1-55379-940-5 7 What Is a Physical Change? Information for Teachers All substances, whether the iron in a coat hanger or the cotton in a shirt, can undergo a physical change. This means the substance keeps its original properties (atoms and molecules) but may change its shape, volume, and/or temperature. For example, the coat hanger can be bent, melted, or frozen, and it would still be made of iron. Similarly, if you remove a cotton shirt from a hanger and fold it to pack into a suitcase, you have temporarily altered the form of the shirt, but the substance and its properties remain the same. 21 st Century Competencies Critical Thinking and Communication: Students will look at various phenomena and determine if a physical change has occurred. They will then analyze the situation to see if the change is reversible or not.

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