Caloimetry and Molar Enthalpy

To measure heat absorbed/ released by water, we need to know:

• Temperature change (° C)
• Amount of Water (g, kg, mL, L)
• Specific Heat Capacity (kJ/kg ° C)- the heat needed to change 1 degree C in 1 kg

Example:
Calculate the amount of heat required to warm 400g of water from 20°C to 50°C.

ΔH = mCΔT
ΔH = (0,400kg)(4.19kJ/kg x T)(30°C)
ΔH = 50 kJ

Molar Enthalpy
- Heat absorbed / released by one mole

Example:
When a candle (C25H25) is burnt, heat is released according to the following reaction:

C25H52 + 38O₂ → 25CO₂ + 26H₂O +1100kJ

If 1.0g of wax is burnt, how much energy is released?

1.0g (mol / 352g)
= 0.00284mol

0.00284mol × 1100kJ / 1molC25H52
= 31.2 kJ/mol

Therefore: 31.2 kJ/mol of energy are released when 1.0g of wax is burnt

HEAT AND ENTHALPY

HEAT AND ENTHALPY

Ø Reactions that release heat are exothermic

Ø Reactions that absorb heat are endothermic

Ø Heat is a form of energy

Ø ENTHALPY - Stored energy

Ø Enthalpy of gasoline > Enthalpy of water

Ø Enthalpy symbol is H and change in enthalpy is ΔH

ENTHALPY GRAPHS:

EXAMPLES:
EXOTERMIC-
2C8H18 + 25O2 -----> 16 CO2 + 18H2O + 5076 kJ
2C8H18 + 25O2 -----> 16 CO2 + 18H2O ΔH= - 5076 kJ
ENDOTHERMIC-
3.2 C + 2H2 + 52.3 kJ -----> C2H4
3.2 C + 2H2 + -----> C2H4 ΔH= - 5076 kJ

MORE Practice:
State whether each of the following are exothermic or endothermic.
a.) H + Cl ---> HCl + 432 kJ EXOTHERMIC
b.) 12CO₂ + 11H₂O ---> C1₂H₂2O11 + 12 O1₂ ΔH= 5638kJ ENDOTHERMIC

jan 8 - types of chemical reactions

1) Synthesis

A+B ----> C (Two or more substances combine)
EX: H2 + Cl2 ----> 2HCl

6) Combustion


AB---->A+B (Breaking down into simpler substances)
EX: 2Ag2O---->4Ag + O2

3) Single Replacement

A + BX---->B + AX (Compunds must have a metal and a nonmetal-replacing one atom in a compound by anohter atom)
EX: Cl2 + 2KI ----> I2 + SKCl

4) Double Replacement

AB + XY ----> AY + XB (exchange of atoms between two different compounds)
EX: 2NaCl+ H2SO4 ----> 2 HCl + Na2SO4

5) Neutralization

(Products are water and an ionic salt/ Always between acids and bases)
EX: HCl + NaOH----> NaCL + H2O

6) Combustion

There are two types: Metallic (Can also be known as a synthesis reaction/includes oxygen) and hydro-carbon (includes carbon and oxygen). Also, the productes are always CO2 and H2O

EX: C5H12 + 8 O2 ----> 5CO2 + 6 H2O

Jan 6

Jan 6 - First class back from christmas break

Balancing with C, H, & O

1.) CH4 + O2 ---> CO2 + H2O
CH4 + O2 ---> CO2 + 2H2O
2.) CHH6 + O2 ---> CO2 + H2O
2CHH6 + 7O2 ---> 4CO2 + 6H2O
3.) C8H18 + O2 ----> CO2 + H2O
2C8H18 + 25O2 ----> 16CO2 + 18H2O

ALCOHOLS:
- Octane = most important chemical used to dilate fuel gas for cars
- OH means alcohol (Ex. C2H5OH = ethane)

Examples:
1.) CH3OH + O2 ---> CO2 + H2O
2CH3OH + 3O2 ---> 2CO2 + 4H2O
2.) C2H5OH + O2 ---> CO2 +H20
C2H5OH + 3O2 ---> 2CO2 +3H20

WORDS TO BALANCED EQUATIONS:

Example 1:
Aluminum chloride is mixed with potassium carvbonate. Aluminum carbonate and potassium chloride are formed.
Write the equation and balance:
AlCl3 + K2CO3 -----> Al2(CO3)3 + KCl
2 AlCl3 + 3 K2CO3 -----> 1 Al2(CO3)3 + 6 KCl

Example 2:
Aluminum metal reacts violently with bromine to produce aluminum bromide.
Al + Br2 -----> AlBr3
2 Al + 3 Br2 -----> 2 AlBr3

Example 3:
Magnesium sulphate hepta hydratee decomposes to form water and magnesium sulphate.
MgSO4 - 7 H2O -----> MgSO4 + 7 H2O


Acids - NEED TO KNOW:
HCl - Hydrochloric Acid
HNO3 - Nitric Acid
H2SO4 - Sulphuric Acid
H3PO4 - Phosphoric Acid
CH3COOH - Acetic Acid

EXTRA Practice:
1.) NH3 + O2 ---> NO + H2O
4NH3 + 5O2 ---> 4NO + 6H2O
2.) (NH4)2C2O4 + AlCl3 ---> Al2(C2O4)2 + NH4Cl
3(NH4)2C2O4 + 2AlCl3 ---> Al2(C2O4)2 + 6NH4Cl

3.) aluminum metal reacts with bromine to form aluminum bromide
2Al + 3Br ---> 2AlBr3