Thermo Basics
What is the symbol for heat/energy?
What's the difference between endothermic and exothermic processes?
Endothermic = absorbs heat/energy
Exothermic = releases heat/energy
What equation or values can be used to calculate heat changes on the sloped parts of a heating/cooling curve?
q = mcΔt
What equation or values can be used to calculate heat changes on the flat parts of a heating/cooling curve?
Heat of vaporization (ΔHvap) or Heat of fusion (ΔHfus)
How many joules are in 1 cal?
4.18 J
Define system v. surroundings.
System = defined part of the universe being studied
Surroundings = everything around the system
Endothermic or Exothermic: In a system, the temperature when two substances were mixed.
Exothermic
If you were to calculate the energy required to heat ice below its melting point to water vapor above its boiling point, how many separate calculations would be needed to account for the total energy?
5
The temperature of 0.044 kg of iron (ciron = 0.45 J/g °C) dropped from 98°C to 23°C. Calculate q in Joules.
-1,485 J
List the melting/freezing point and boiling/condensing point of water AND which ΔH value goes with each phase change.
Melt/Freeze = 0°C, ΔHfus "Heat of Fusion"
Boil/Condense = 100°C, ΔHvap "Heat of Vaporization"
What is the 1st Law of Thermodynamics?
Energy cannot be created or destroyed, only transferred between a system and surroundings.
Endothermic or Exothermic: Phase changes on a cooling curve.
Exothermic
There are 160 Cals in 21 cheese puffs (per serving food Label). Determine the number Joules in 1 cheese puff.
31,847.6 J
List all 3 ways you may have to manipulate steps/stages of an equation to get the overall equation (Hess's Law).
Multiply, Divide, Reverse/Flip
Explain using particle behavior, the difference between thermal energy and phase energy.
Thermal energy = measures particle speed
Phase energy = changing space between particles
What is the measurement of total heat energy in a thermodynamic system called? Also known as the "heat of a reaction"...
Enthalpy (H)
When two substances were mixed, the q value of the solution was -888 J. What would the q value of the reaction be, and is this process endothermic or exothermic?
+888 J, endothermic
Given the following data:
SrO + CO2 ---> SrCO3 ΔH = −234 kJ
2 SrO ---> 2 Sr + O2 ΔH = +1184 kJ
2 SrCO3 ---> 2 Sr + 2 C + 3 O2 ΔH = +2440 kJ
Find the ΔH of the following reaction:
C + O2 ---> CO2
-394 kJ
How much energy is needed for the reaction of 1.22 moles of H3BO3 with 5.68 g moles of hydrogen?
2 H3BO3 + 6 H2 + 493 kJ 🡪 B2H6 + 6 H2O
231.01 kJ
What is the name of the phase change going from a gas straight to a solid?
Deposition
Explain why energy is required/absorbed during a phase change on a heating curve.
Change space between particles - breaking IMFs requires energy!!!
Organize these scenarios into endothermic or exothermic:
Snowman melting
Products are lower in energy than the reactants
Heat as a reactant
Cold pack
Breaking chemical bonds
Water condensing on water bottle
Endothermic: snowman melting, heat as a reactant, cold pack, breaking chemical bonds
Exothermic: products are lower in energy than the reactants, water condensing on water bottle
When a 10.6 g sample of KCl dissolves in 44.0 g of water (cwater= 4.18 J/g°C) in a calorimeter, the temperature drops from 52.2 °C to 30.6 °C. Calculate q for the process (i.e. solution and reaction) in Calories. Is the reaction endothermic or exothermic?
qsol = -1.18 Cal
qrxn = +1.18 Cal
Endothermic
A 11.54 g sample of an unknown metal is heated to 95.5 °C and then is plunged into 20.0 g of water (cwater= 4.18 J/g°C) at 23.4 °C. The temperature of the water rose to 30.1°C. What is the specific heat of the metal?
c = 0.742 J/g°C
What is the name of the phase change going from a solid straight to a gas?
Sublimation