7.9 Review – Reactions

Define chemical equation A chemical equation is a symbolic representation of a chemical reaction.

How are chemical symbols written 1 or 2 letters, first one is capitalized, 2nd one is not.

What is a chemical formula A chemical formula shows the elements and number of atoms of each element in a molecule/compound

4. What is a subscript? The subscript describes the number of atoms of a particular element. It applies to the element symbol directly in front of it. H2O

The coefficient is a number in front of the formula. 5. What is a coefficient? The coefficient is a number in front of the formula. It shows the number of molecules of that compound It applies to everything that follows it until you get to a + or 

6. What are the two halves of the equation called? Reactants- the combination of chemicals before the reaction takes place (left of arrow) Products- combination of chemicals after the reaction takes place (right of arrow)

C12H22O11 C = 12 H = 22 O =11 Cu2CO3 Cu = 2 C = 1 O = 3 7. Atom counts: C12H22O11 C = 12 H = 22 O =11 Cu2CO3 Cu = 2 C = 1 O = 3

4NH3 N = 4 H = 12

8. Atom Counts 2NH3 + O2 NO2 + H2O N = 2 N = 1 H = 6 H = 2 O = 2 O = 3

b. C8H18 + O2  CO2 + H2O C = 8 C = 1 H = 18 H = 2 O = 2 O = 3

9. State the law of conservation of matter In a chemical reaction, matter cannot be created or destroyed.

How do you know if an equation is balanced or not? Do the atom count

Rules for balancing equations: Do atom count Only change coefficients, NOT subscripts Recount!

12. Balance: ________C + ________O2  ________ CO 2,1,2

________H2 + ________O2  ________ H2O 2,1,2

________Mg + ________O2  ________ MgO 2,1,2

13. What is nuclear chemistry? The study of the structure of atomic nuclei and the changes they undergo.

14. List 4 characteristics of nuclear reactions Chemical Nuclear Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, just rearranged Atoms often converted into atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons Associated with small energy changes Large energy change

15. List the achievement of each of the following: Becquerrel – discovered radiation Marie and Pierre Curie – studied radioactivity from the 1800’s into the 1900’s Roentgen – discovered X-Rays

16. What is a half life? Half-life is the time required for half of a radioisotope’s nuclei to decay into its products.

17. What % of any r.i. would be left after 4 half-lives? % remaining 100 % 1 50 % 2 25 % 3 12.5 % 4 6.25 % 5 3.125 % 6 1.5625%

18. Describe fission A fission reaction splits up a large nucleus into smaller pieces, energy is released

19. Describe fusion. A fusion reaction is a nuclear reaction that combines or fuses two smaller nuclei into a larger nucleus, energy is released

20. List 4 uses of radiation: Radioactive dating Radiation for cancer cells X-rays Medical tests using tracers (radioactive dyes) Sterilizing equipment using radioactive rays

21. 12.5 grams 22. 6.25 grams 23. 50 grams 24. 25 days.

25. Describe the following: Alpha particle – a particle of two protons and two neutrons that comes from a radioisotope. Often referred to as a Helium Nucleus. Beta Particle – an electron emmitted from the nucleus of a radioisotope. Gamma Rays – a form of radiation that is a powerful electromagnetic wave

What is a Geiger Counter? Geiger Counter – a device that measures radioactivity by producing an electric current when radiation is present.

27. What is The Strong Force? The force in the nucleus that cuases protons and neutrons to attract to one another.