science

2. Thermochemistry
 Thermochemistry is the relationship
between chemical reactions and
energy changes.
 Thermal energy transferred between 2
bodies that are at different
temperatures.
 1 calorie = 4.186 J

3. The System and It’s
Surroundings
 A system is a specific part of the
universe that is of interest.
 Everything outside the system is the
surrounding.

4. Types of Systems
 An open system can exchange mass
and energy.
 A closed system allows the transfer of
energy but not mass.
 An isolated system does not allow the
transfer of either the mass or energy.

5.  When two systems with different
temperature interact, these systems will
approach a common new temperature
that is somewhere between the initial
temperatures to attain thermal
equilibrium.

6. HEAT AND
TEMPERATURE
 The flow of energy from a body at higher
temperature to one at lower temperature
is known as heat.
 Temperature is the average internal
kinetic energy of particles in the system.
 Temperature is the indicator of thermal
equilibrium.
 Temperature plays a role in determining
the rate and extent to which a chemical
reaction occurs.

7. EXOTHERMIC AND
ENDOTHERMIC PROCESSES
 Exothermic Process : Q = (-)
- Heat is transferred from the system to
the surroundings.
 Endothermic Process : Q = (+)
- Heat is transferred from the
surroundings to the system.

8. EXOTHERMIC AND
ENDOTHERMIC PROCESSES
 Exothermic Process : Q = (-)
- Heat is transferred from the system to
the surroundings.
 Endothermic Process : Q = (+)
- Heat is transferred from the
surroundings to the system.

9. ENTHALPY AND CHEMICAL
REACTIONS
 Enthalpy is an extensive property where its
magnitude depends on the amount of substance
present.
 The enthalpy of reaction, ΔH, is the difference
between the enthalpies of the products and the
enthalpies of the reactants.
ΔH = H(products) – H(reactants)

10. THERMOCHEMICAL
EQUATIONS
 The stochiometric coefficients always refer to the
number of moles of a substance.
 Reversing the equations means changing the roles of
reactants and products.
 Always specify the physical states of all the reactants
and products when writing thermochemical equations.

11. H2O(S)
Consider the following equations:
CH4(g)
ΔH = 6.01 kJ
H2O(l)
O2(g) CO2(g)
H2O(l)
ΔH = - 890.4 kJ

12. HESS’S LAW OF HEAT
SUMMATION
 To determine the change in entalphy of the desired
reaction, Hess’s law is applied.
 Hess’s law state that when reactants are
converted to products, the change in enthalpy is
the same whether the reaction takes place in one
step or in series of steps.

13. CALIOMETRY
 Caliometry is the quantitatvie
measurement of the heat required
during a chemical process.
 Calorimeter is an instrument used to
measure heat chnages.

14. Q =
mcΔT
 The amount of heat required to raise the
temperature of 1 gram of the substance
by 1°C.
Specific Heat Capacity (c)

15. Q = sΔT
 The amount of heat required to raise the
temperature of a given amount of
substance by 1°C.
Heat Capacity (s)

16. Does water has
a high specific
heat capacity?