Heat flows _________ the system and _________the surroundings
Temperature goes _______
Only look at heat (q) to determine if the system is endo or exo
EnthaIpy (H) is a state function equal to E +pV
DH = DE + D (pV), with constant pressure,
DH = DE + p DV is equal to the expression for q at ____________. Therefore, at constant pressure DH = qp. This means that the change in enthalpy is equal to the heat flow. DH = H final - H initial = qp
Enthalpy of reaction: DH = ___________________
When Δ H is negative, heat is ___________the system and the reaction is ____________.
When Δ H is positive, heat is ______ to the system and the reaction is ___________.
When 1 mole of methane is burned at constant pressure, 890 kJ of energy is released as heat. Calculate the ΔH for a process in which a 5.8 g sample of methane is burned at constant pressure.
Specific Heat (c) – the amount of _____________ to raise the temperature of 1 g of a substance 1 °C
The units for specific heat are ______
The specific heat of water (in a liquid form is _________)
A 58.0 g sample of a metal at 100.0 °C is placed in a calorimeter containing 60.0 g of water at 18.0 °C. The temperature of that water increases to 22.0 °C. Calculate the specific heat of the metal.
A piece of metal with a mass of 4.68 g at 135°C is placed in a calorimeter with 25.0 g of water at 20.0 °C. The temperature rises to 35.0 °C. What is the specific heat of the metal?
3.25 g Mg is placed into 125 mL of HCl. The initial temperature of the calorimeter is 18.5°C & the final temperature is 26.6°C. If the heat capacity of the calorimeter is 4.86 J/g°C, calculate the enthalpy of the reaction.
c= heat capacity, the energy required to change the temperature of the bomb 1°C
Heat of Formation
Heat of Combustion
Hess's Law -the Heat of Reaction, Enthalpy (ΔH) of a reaction is the sum of the _____________ for each step of the reaction _______ .
Hess’s Law (cont’d)
ΔHfº for Step #1
+ ΔHfº for Step #2
+ ΔHfº for Step #3
ΔH for the reaction
Look at the example below.
Try this one.
= (-790 kJ) - (-196 kJ)
= -594 kJ
for 1 mole of S02,
ΔHo= 1/2 ( -594 kJ) = -297 kJ
Heats of Formation
Heat of Formation (Hf) -amount of energy needed to form _________________.
Standard Heat of Formation DHf°- Heat of Formation at _______________.To determine the amount of energy needed to decompose a reactant, ______________________, The more negative the ΔHfº, the more stable the compound.
Sign changes (if any) for reactions.
For the reaction A + B →C, A and B are__________- change the sign for ΔHfº.
C is _______ -keep the sign for ΔHfº.
ΔHfº for any free element (H2, 02, Zn, S, AI etc.)= _____