Whole class detention on
Friday because of those who
didn’t do homework
REVIEW
COMBUSTION
• ______________
is a process in which a selfsustaining chemical reaction occurs at
temperatures above those of the surroundings.
• EXOTHERMIC = RELEASES HEAT
• ENDOTHERMIC = ABSORBS HEAT
• ________________
= is a measure of the total
ENTHALPHY
energy possessed by a substance or group of
substances.
REVIEW
• What is the equation for ∆H ?
ΔH = enthalpy of products – enthalpy of reactants
• Is the following reactions endothermic or
exothermic? EXPLAIN
–
–
–
–
2SO2( g) + O2( g) → 2SO3( g)
CH4( g) + H2O( g) → CO( g) + 3H2( g)
NH3(aq) + HCl(aq) → NH4 +(aq) + Cl–(aq)
Ag+(aq) + I–(aq) → AgI(s)
∆ H = –198 kJ/mol
∆ H = +206 kJ/mol
∆ H = –52 kJ/mol
∆H = –112 kJ/mol
REVIEW
• Is the following reaction endothermic or
exothermic?
2N + 6H
N2 + 3H2
2NH3
• What formula for ∆H would you use in this
circumstance?
∆ H = (energy to break reactants) – (energy to make product)
TEMPERATURE
• Temperature is a measure of the degree of hotness or
coldness of an object or substance. The hotter the
object, the higher its temperature.
• If two objects or samples of material are brought into
contact, heat will flow from the hot object to the cold one
until the temperature of the two objects is equal.
• When the temperature is uniform throughout both
objects or samples of material, we say that thermal
equilibrium has been reached.
Quantity of Heat
• Two objects can be at the same
temperature but contain very different
amounts of heat.
EXPERIMENT 1
• Three well-insulated beakers each contain
100 g of water at 25.0°C.
The quantity of heat depends upon mass, and nature of substance,
Factors Effecting Quantity of
HEAT
• The amount of heat energy is proportional
to the mass of the substance involved.
• The amount of heat energy contained in
equal masses of different substances
depends upon the nature of the
substances involved.
SPECIFIC HEAT CAPACITY
Units = joules per kelvin per gram, (J/Kg) (J K-1 g-1).
Calculating Quantities of Heat
Specific heat capacities allow us to calculate the quantities of heat that flow
from one object or substance to another.
Where:
q = quantity of heat involved
m = mass of substance
C = specific heat capacity
∆ T = change in temperature (Final – Initial)
When q is positive temperature increase
When q is negative temperature decreases
HOMEWORK Check