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Chemical Reactions

Chemical Reactions. There are four observations which indicate a chemical reaction is taking place. Evidence for Chemical Reactions. A gas is released . Gas may be observed in many ways in a reaction from light fizzing to heavy bubbling.

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Chemical Reactions

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  1. Chemical Reactions

  2. There are four observations which indicate a chemical reaction is taking place. Evidence for Chemical Reactions • A gas is released. • Gas may be observed in many ways in a reaction from light fizzing to heavy bubbling. • Shown here is the release of hydrogen gas from the reaction of magnesium metal with acid.

  3. An insoluble solid is produced. Evidence for Chemical Reactions • A substance dissolves in water to give an aqueous solution. • If we add two aqueous solutions together, we may observe the production of a solid substance. • The insoluble solid formed is called a precipitate.

  4. A permanent color change is observed. Evidence for Chemical Reactions • Many chemical reactions involve a permanent color change. • A change in color indicates that a new substance has been formed.

  5. An energy change is observed. Evidence for Chemical Reactions • Examples of a heat energy change in a chemical reaction are heat and light given off.

  6. A chemical equation describes a chemical reaction using formulas and symbols. A general chemical equation is: A + B → C + D In this equation, A and B are reactants and C and D are products. Writing Chemical Equations

  7. When writing chemical equations, we usually specify the physical state of the reactants and products. A(g) + B(l) → C(s) + D(aq) In this equation, reactant A is in the gaseous state and reactant B is in the liquid state. Also, product C is in the solid state and product D is in the aqueous state (water solution). States of Matter in Equations

  8. Here are several symbols used in chemical equations: Chemical Equation Symbols

  9. Reactivity of Metals Lab Results Magnesium Copper Zinc Silver nitrate nitrate nitratenitrate Mg(NO3)2 Cu(NO3)2 Zn(NO3)2 AgNO3 ↓ ↓ ↓ ↓ Magnsium metal Copper metal Zinc metal → → →

  10. Lets look at a chemical reaction that occurred in the metal reactivity lab: Cu(NO3)2(aq) + Zn(s) →Zn(NO3)2(aq) + Cu(s) The equation can be read as follows: Aqueous copper nitrate is added to solid zinc and yields aqueous zinc nitrate and solid copper. Notice zinc replaced copper in the nitrate solution and solid copper formed as a precipitate. A Chemical Reaction

  11. Here’s another chemical reaction that occurred in the metal reactivity lab: 2AgNO3(aq) + Mg(s) →Mg(NO3)2(aq) + 2Ag(s) The equation can be read as follows: Aqueous silver nitrate is added to solid magnesium and yields aqueous magnesium nitrate and solid silver. Notice magnesium replaced silver in the nitrate solution and solid silver formed as a precipitate. A Chemical Reaction

  12. When a metal undergoes a replacement reaction, it displaces another metal from a compound or aqueous solution. The metal that displaces the other metal does so because it is more active. The activity of a metal is a measure of its ability to compete in a replacement reaction. In an activity series, a sequence of metals is arranged according to their ability to undergo reaction. Metal Activity Series

  13. Metals that are most reactive appear first in the activity series. These will replace any metals that are to the right of them. Metals that are least reactive appear last in the activity series. The relative activity series is: Li > K > Ba >Sr>Ca> Na > Mg >Al >Mn> Zn > Fe > Cd > Co > Ni >Sn>Pb>Cu > Ag > Hg >Au Activity Series

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