UNIT 2Chemical Reactions

KEY IDEASVocabulary What does it mean?

intermolecular bond

intramolecular bond

open and closed system

surroundings

word equation

chemical equation

reactant

product

phase

solid

liquid

gas

aqueous

synthesis

decomposition

single replacement

double replacement

neutralization

combustion

endothermic

exothermic

enthalpy

1 Gu 2015

2.0 - Systems

What are chemical reactions? new substances are formed with new properties

( ____________________________________________) some chemical bonds are broken and some new chemical bonds are formed atoms are ______________________

Physical Change Chemical Change

When we study reactions, we talk about systems system: part of the universe being studied

o __________ system: things cannot enter or leave the systemo __________ system: things can enter or leave the system

surroundings: anything outside of the system

System 1 System 2

2 Gu 2015

Chemical reactions in closed systems ALWAYS follow four basic laws:

The Law of...1. Conservation of Mass: total mass in a reaction does not change 2. Conservation of Atoms: the total # and type of atoms does not change3. Conservation of Electrical Charge: the total charge does not change4. Conservation of Energy: the total energy does not change

3 Gu 2015

2.1 - Writing Chemical Equations

Word equation: uses words to describe a reaction

Chemical equation: uses symbols, subscripts, and coefficients to describe a reaction

reactant: substances you begin with product: substances you make in a chemical reaction phase symbols: symbols that tell you what phase the reactants and products are in

o (s) = solido (l) = liquido (g) = gaso (aq) = aqueous (substance dissolved in water)

There are 7 non-metals that exist in nature as __________________________, or molecules with 2 atoms. These are typically gases. Whenever a reaction is done with these elements, the subscript is always 2!

Memorize the 7 diatomic elements!

4 Gu 2015

solid copper (l) carbonate + water → carbon dioxide gas + copper (l) hydroxide

Cu2CO3(s) + H2O(l) → CO2(g) + 2 CuOH(aq)

H2 O2 F2 Br2 I2 N2 Cl2

HOFBrINCl

2.2 - Balancing Chemical Equations

The four conservation laws must be expressed when writing chemical reactions equations

Guideline on how to balance equations1. Check that diatomic molecules are paired. 2. Balance metal atoms first, non-metals next.3. Balance groups of polyatomic ions if possible.4. Balance oxygen and hydrogen last.5. Count that the number of atoms for each element on both sides of the equation are equal.6. Reduce coefficients if possible so you have the smallest ratio.7. If a fraction appears, multiply the equation by the whole number to eliminate the fraction.

Practice: Balance the following skeleton chemical equations

1. ___Ca2C + ___O2 → ___ Ca + ___CO2

2. ___Pb(NO3)2 + ___ NaI → ___PbI2 + ___ NaNO3

3. ____ N2 + _____ H2 → _____NH3

4. ____ KClO3 → ____ KCl + ____O2

5. ____ NaCl + ____ F2 → ____ NaF + ____ Cl2

6. _____ H2 + ___ O2 → ____ H2O

7. _____ AgNO3 + ____ MgCl2 → ____ AgCl + ____ Mg(NO3)2

8. ____ AlBr3 + ___K2SO4 → ___KBr + ___ Al2(SO4)3

9. ____CH4 + ____ O2 → ____ CO2 + ____ H2O

10. ____ C3H8 + ____ O2 → ____ CO2 + ____ H2O

11. ____ C5H12 + ____ O2 → ____ CO2 + ____ H2O

12. Challenge: ____ C19H17NO3 + ____ O2 →____ CO2 + ____ H2O + ____ N2

5 Gu 2015

Practice: Write and balance the following reactions.

1. Sodium ion reacts with sulphate ion to produce sodium sulphate.

2. Boron mononitride reacts with fluorine to give boron trifluoride and nitrogen

3. Solid sodium reacts with chlorine gas to produce solid sodium chloride.

4. Liquid water reacts with powdered sodium oxide to produce aqueous sodium hydroxide.

6 Gu 2015

2.3 - Six Major Types of Chemical Reactions

1. synthesis (or combination): A + B → AB two or more elements combine to form a compound

2. decomposition: AB → A + B a single compound breaks down into simpler substances (“reverse synthesis”)

3. single replacement: A + BY → B + AY an element reacts with a compound, one element replaces another (like with like)

4. double replacement: AX + BY → BX + AY two compounds react, two elements switch places (like with like)

5. combustion: CaHbYc + O2 → H2O + CO2 an organic compound (compound with C and H) reacts with O2 to produce heat (fire), H2O, and CO2

6. neutralization: HA + BOH → H2O + AB an acid reacts with a base (molecule with OH) to produce water and salt

7 Gu 2015

2.4 - Energy Changes

Enthalpy (H): ________________________________ contained in a system

In a chemical reaction, there is BOTH bond breaking AND bond making bond breaking: _____________________ bond making: _____________________

Net total energy change for a reaction is:

Endothermic Exothermic

energy bond breaking _____ energy bond making energy is a _______________ energy of products _____ energy of reactants H = Hproduct – Hreactant = ________________ on a graph

HCl + 50kJ → H+ + Cl-

H =

energy bond breaking _____ energy bond making energy is a _______________ energy of products _____ energy of reactants H = Hproduct – Hreactant = ________________ on a graph

H+ + Cl- → HCl + 50kJ

H =

8 Gu 2015

Practice

Draw an energy diagram for a reaction with H = +25 kJ. This reaction is __________________

Draw an energy diagram for a reaction with H = -50 kJ. This reaction is __________________

Draw an energy diagram for A + B + 20 kJ → C. This reaction is __________________

9 Gu 2015