Vocab
"The study of heat changes in chemical reactions and physical changes."
Thermochemistry
How much heat is required to raise 475 grams of water temperature from 20 to 30oC?
4,750 calories
"A chemical equation which includes the energy used or produced in a chemical reaction."
(All reactions involve energy changes!)
Thermochemical equation
2C2H6 + 7O2 -> 4CO2 + 6H2O
(heat change = -1,559.7 kJ)
If 1 mole of each reactant is used, what is the limiting reactant based on energy production?
oxygen (O2)
You accidentally leave your back door open during winter (0oC outside, 23oC inside). What is the best explanation as to why your house gets colder?
A. The cold air flows into your house from outside.
B. The warm air in your house leaves and flows outside.
C. Some magical pixie fairies were blowing kisses into your house.
D. Politicians.
B. The warm air in your house leaves and flows outside.
"The ability to do work, cause change, or supply heat."
Energy
DAILY TRIPLE! 200 points each!
What 3 things are the amount of heat (absorbed or released during a change) dependent upon?
1. mass
2. temperature change
3. the substance (its specific heat)
2C2H6 + 7O2 -> 4CO2 + 6H2O
(heat change = -1,559.7 kJ)
Is the combustion of ethane (C2H6) endothermic or exothermic?
Exothermic (negative heat change -1,559.7 kJ)
2C2H6 + 7O2 -> 4CO2 + 6H2O
(heat change = -1,559.7 kJ)
If 1 mole of each reactant is used, how much energy is produced?
- 222.9 kJ
1. Give 2 different Metric units of heat.
2. Give a numerical relationship between these 2 units.
1. calories (cal) and Joules (J)
2. 1 cal = 4.18 J
Give 3 examples of energy.
chemical, electricity, heat, hydro, kinetic, magnetic, mechanical, nuclear, potential, solar, sound, wind...
(and more!)
What mass of water would go from 50 to 75oC when heated with 5,000 J of heat?
47.85 g
2C2H6 + 7O2 -> 4CO2 + 6H2O
(heat change = -1,559.7 kJ)
How much energy is released when 7.5 moles of ethane (C2H6) is burned?
- 5,848.88 kJ
2C2H6 + 7O2 -> 4CO2 + 6H2O
(heat change = -1,559.7 kJ)
If 100 g of each reactant is used, how many kJ of energy is produced?
696.3 kJ
DAILY TRIPLE! 300 points each!
1. What is the term for heat that is being RELEASED during a chemical reaction?
2. Would this be represented by a positive or negative numerical value?
3. What side of a chemical equation would you see this energy change on?
(reactants < or products >)?
1. exothermic
2. negative (-)
3. products (>)
Heat flows until all objects in the mixture reach __.
HINT: when you put the hot metal in the cold water, their temperatures "met in the middle"
Equilibrium
"The heat content of a substance at constant pressure."
Enthalpy (H)
2C2H6 + 7O2 -> 4CO2 + 6H2O
(heat change = -1,559.7 kJ)
How many grams of ethane (C2H6) are required to produce 3,000 kJ of energy?
115.4 g C2H6
2C2H6 + 7O2 -> 4CO2 + 6H2O
(heat change = -1,559.7 kJ)
If 2.2 mol ethane reacts with 8.1 mol O2 , how much energy (kJ) will be produced?
1715.7 kJ
Convert 123 kJ to calories (cal).
29,426 calories
What will be the final temperature of 500 g of steel (specific heat of 0.115 cal/goC) if it begins at room temperature (23oC) and is heated with 5,000 calories of heat?
86.96oC + 23oC = 109.96oC
2C2H6 + 7O2 -> 4CO2 + 6H2O
(heat change = -1,559.7 kJ)
How much heat (kJ) is required to produce 2,323 g of water vapor?
33,544.4 kJ
DAILY DOUBLE! 500 POINTS EACH!
What is the...
1. heat of fusion for water (in cal/goC)?
2. heat of vaporization for water (in cal/goC)?
1. 80 cal/goC
2. 540 cal/goC
"Energy cannot be created or destroyed, only changed."