Chemical Reactions

Vocabulary  substance  compound  chemical bond  chemical formula  chemical reaction  reactant  product  coefficient  ionic bond  covalent bond  polar molecule  nonpolar molecule

Substance Matter that is an element or a compound.

Compound The combined atoms of two or more elements.

Chemical Bond Force that holds together atoms in a compound.

Chemical Formula A precise statement that tells which elements are in a compound and their ratios.

Chemical Reaction Change in which one or more substances are converted to different substances.

Reactant Starting substance in a chemical reaction.

Product Substance produced by a chemical reaction.

Coefficient Represents number of units of each substance in a chemical reaction.

Ionic Bond Attraction between opposite charges of ions in an ionic compound. Salt is an example. Na + Cl → [Na] + [Cl] - → NaCl

Covalent Bond Shared electrons between atoms which form molecules. Carbon dioxide is an example. C + O 2 → CO 2 COOCOO → +

Covalent Bond Let’s look at valence electrons using dot diagrams. C + O 2 → CO 2 COOCOO → + C + O O → O C O

Polar Molecule Molecule with opposite charges on each end. Water is an example. H 2 O O H H ++ -

Nonpolar Molecule Molecule without opposite charges on each end. Nitrogen is an example. N 2 NN

16.1: Chemical Changes in Matter  Please turn to page 442

Describing chemical reactions  In a chemical reaction, one or more substances change into new substances!

Describing chemical reactions  The substances before the reaction occurs are called reactants.  The substances after the reaction occurs are called products. reactants → products

Photosynthesis: a chemical reaction reactants → products carbon dioxide + water → sugar + oxygen 6CO 2 + 6H 2 O + light → C 6 H 12 O 6 + 6O 2 coefficient

Conservation of mass Mass is conserved in a chemical reaction. Atoms are neither created nor destroyed.

Writing chemical equations lead nitrate + potassium iodide → lead iodide + potassium nitrate Pb(NO 3 ) 2 + 2KI → PbI 2 + 2KNO 3 ++

Coefficients Coefficients represent the number of units of each substance taking part in the chemical reaction. Pb(NO 3 ) 2 + 2KI → PbI 2 + 2KNO 3 This is the same as Pb(NO 3 ) 2 + (KI + KI) → PbI 2 + (KNO 3 + KNO 3 )

Balancing equations What coefficients need to be added? H 2 + O 2 → H 2 O Indicate the reactants and products.

Balancing equations What coefficients need to be added? Mg + O 2 → MgO Indicate the reactants and products.

Balancing equations What coefficients need to be added? AgNO 3 + NaCl → AgCl + NaNO 3 Indicate the reactants and products.

Balancing equations What coefficients need to be added? Ag + H 2 S → Ag 2 S + H 2 Indicate the reactants and products.

Balancing equations What coefficients need to be added? MgCl 2 + Na 2 CO 3 → MgCO 3 + NaCl Indicate the reactants and products.