USC Bridge 1.4 chemical reactions

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1

Chemical reactions

Occur when chemical bonds are formed, rearranged, or broken.

Can be written as chemical equations

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Chemical equations contain:

Reactants-substances entering into a reaction together

product- resulting chemical end products

amouunts of reactants and products are shown in balanced equations

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Molecular formula

Subscripts show how atoms are joined by bonds

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Three main types of chemical reactions

  • Synthesis
  • decomposition
  • exchange
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Synthesis reactions

When atoms or molecules combine to form a larger more complex molecule

Anabolic reactions: A+B-> AB

always Involves bond formation

ie: amino acids form a protein molecule

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Decomposition reaction

Bonds are broken in larger molecules, resulting in smaller less complex molecules or constituent atoms (reverse of synthesis reactions).

Involve catabolic (bond breaking) reactions AB-> A+B

glycogen is broken down to release glucose molecules. Fats are digested in the small intestine by decomposition reactions..

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Exchange reactions ( displacement reactions)

Bonds are both made and broken, involves synthesis and decomposition.

Parts of the reactant molecules change partners producing different product molecules

ATP transfers phosphate group to glucose to form glucose-phosphate

AB+C->AC+B

and AB+CD->AD+CB

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Oxidation reduction (redox) reactions

The gain of oxygen or loss of hydrogen atoms and their electrons.

  • Oxidized substances lose electrons and energy (electron donor)
  • reduced substances gain electrons and energy (electron acceptor)

different from ionic bonds bonds as electrons are lost entirely

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Exergonic

Reactions that release energy

  • products have less potential energy than reactants
  • catabolic and oxidative reactions ie breaking down a large molecule into smaller ones gives off energy
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Endergonic

Energy absorbing reactions that contain more potential energy in their chemical bonds than did the reactants

  • products have more potential energy than reactants
  • anabolic reactions
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Reversibility of chemical reactions

All chemical reactions are theoretically reversible.

  • Chemical equilibrium occurs if neither a forward nor a reverse reaction is dominant
  • many biological reactions are not very reversible because energy requirements to go backward are too high or products have been removed
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Rate of chemical reactions are affected by:

Temperature

concentration

particule size

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Catalysts

Increase the rate of a reaction without being chemically changed or becoming part of the product

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Enzymes

Biological catalysts. Separate proteins that help a reaction. Not part of the reaction and not changed during the reaction

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In a chemical reaction _______ join to form _____

Reactants products

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What will be the effect on a chemical reaction if the concentration of reactants is increased?

The speed of the reaction will increase

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Building muscle tissue is an example of:

Synthesis