First Law of Thermodynamics
Gases A(g) and B(g) are confined in a cylinder-piston arrangement and react to form a solid product C(s):
A(g) + B(g) → C(s). As the reaction occurs, the system loses 1150 J of heat to the surroundings. The
piston moves downward as the gases react to form a solid. As the volume of the gas decreases the gas
decreases under the constant pressure of the atmosphere, the surroundings do 480 J of work on the
system. What is the change in the internal energy of the system?
-670 J
How many grams of water can be heated from 20.0 oC to 75oC using 12500.0 Joules
54.32 g
The complete combustion of ethanol, C2H5OH, proceeds as follows:
C2H5OH(l) + 3 O2(g) → 2 CO2(g) + 3 H2O(l)
∆H = -555 kJ
What is the enthalpy change for the combustion of 15.0 g of ethanol?
-181 kJ
What is the equation for ΔH°rxn?
ΔH°rxn= (Sum of ∆Hf° Products)-(Sum of ∆Hf° Products)
Give me 3 properties of gases
1. Gases expand to take the shape of their container. They completely and uniformly
occupy the volume of any container.
2. Gases are fluid – particles easily flow past one another.
3. Low Density – A substance in the gaseous state has 1/1000 the density of the same
substance in the liquid state.
Units of gas density – g/L
4. Gases can be compressed, decreasing the distance between particles, and therefore
decreasing the volume occupied by the gas.
5. Gases exert pressure on their surroundings.
6. Gases diffuse into one another, so samples of gas placed in the same container mix
completely to become a homogeneous mixture.
A system absorbs 140 J of heat from the surroundings and does 85 J of work on the surroundings.
+58 J
What is the final temperature after 840 Joules is absorbed by 10.0g of water at 25.0oC?
45.1 oC
Hydrogen peroxide can decompose to water and oxygen by the reaction
2 H2O2(l) → 2 H2O(l) + O2(g) ∆H = -196 kJ
Calculate the quantity of heat released when 5.00 g of H2O2(l) decomposes at constant pressure.
-14.4 kJ
What does Hess' Law do?
Manipulates equations
What is Boyle's law?
Increasing volume, decreases pressure
Decreasing volume, increases pressure
Inverse Relationship
P1V1=P2V2
What is an open, closed and isolated system?
Open: A system where matter and heat can escape.
Closed: A system where matter can't escape but energy can.
Isolated: A system where both matter and energy can't escape.
What is the specific heat of aluminum if the temperature of a 28.4 g sample of aluminum is increased by 8.1 oC when 207 J of heat is added?
0.9 J/goC
Consider the following reaction:
2 Mg(s) + O2(g) → 2 MgO(s) ∆H = -1204 kJ
Is this exothermic or endothermic?
Exothermic
Calculate the ΔH°rxn for the following reaction
2 HCl(aq) + Zn(s) → ZnCl2(aq) + H2(g)
HCl(aq) -167.2
Zn(s) 0
ZnCl2(aq) -415.1
H2(g) 0
-80.7 kJ
A 3.50 L sample of hydrogen gas has a pressure of 0.750 atm. What is its volume if its pressure is increased to 1.50 atm at constant temperature?
1.75 L
What are the units of molar heat capacity and specific heat capacity?
J/mol, J/g(C0)
What is the specific heat of silicon if the temperature of a 4.11 g sample of silicon is increased by 3.8 oC when 11.1 J of heat is added?
0.71 J/goC
Consider the following reaction:
2 Mg(s) + O2(g) → 2 MgO(s) ∆H = -1204 kJ
Calculate the amount of heat transferred when 3.55 g of Mg(s) reacts at constant pressure.
-87.9 kJ
Calculate the ΔH°rxn for the following reaction
4 FeO(s) + O2(g) → 2 Fe2O3(s)
FeO(s) -271.9
O2(g) 0
Fe2O3(s) -822.2
-556.8 kJ
A 678 mL sample of helium gas, initially at 0°C, is heated at constant pressure. If
the final volume of the gas is 0.896 L, what is its final temperature in °C?
88oC
Which direction does heat move?
How much heat is lost when 32 g of iron cools from 160 oC∘C to 40 oC? The specific heat for iron is 0.45J/goC
1.73J ×103
Consider the following reaction:
2 Mg(s) + O2(g) → 2 MgO(s) ∆H = -1204 kJ
How many kilojoules of heat are absorbed when 40.3 g of MgO(s) is decomposed into Mg(s) and O2(g) at
constant pressure?
+602 kJ
Determine ΔH (enthalpy change) for the following reaction.
5CO2(g) + Si3N4(s) → 3SiO(s) + 2N2O(g) +5CO(g)
given:
CO(g) + SiO2(s) → SiO(s) + CO2(g) ΔH = +520.9 kJ
given:
3SiO2(s) +2N2O(g) + 8CO(g) → 8CO2(g) +Si3N4(s) ΔH = -461.1 kJ
+2023.8 kJ
Calculate the volume of 1.63 mol carbon dioxide gas at 295 K and 1.14 atm?
34.6 L