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Name ______________________________________
Period ____________
Chapter 10
Causes of Change
10-1 Energy Transfer
1. Heat - _____________ that is transformed from one object to another due to a
difference in ____________________. (symbol for heat - )
2. Temperature – a measure of the average ___________ energy of the particles in a
substance. Temperature is an __________ property, and heat is a ___________
property.
3. Thermochemistry – the study of ___________________________ in a chemical
reaction.
4. Types of Chemical Reactions
a. Exothermic Reactions - ________________ heat into their surroundings
-Heat is a ________________ of the reaction.
-combustion reactions are exothermic
-C3H8 + 5O2
→
3CO2 + 4H2O + 2043 kJ
b. Endothermic Reactions – heat is ________________ by the reactants and
stored in the ________________________ of the product.
-Heat acts as a _____________________.
-C + H2O +113kJ → CO + H2
5. Molar Heat Capacity
-
The heat absorbed or released during a reaction depends on a difference in quantity
called ________________. (Total ____________ content of a sample)
-The symbol for enthalpy is _______.
-When reactions take place at standard temperature and pressure, _____ = ______.
Standard temp. =
Purest form of substance =
Standard pressure =
Enthalpy change at STP is denoted
1) Enthalpy Change (ΔH = H products – H reactants)
ΔH
H products
H reactants
Exothermic
Reaction
Endothermic
Reaction
2) Enthalpy Diagram
C(s) + H2O(g) → CO(g) + H2(g)
a. Which has a higher enthalpy? Products or Reactants
b. Was heat absorbed or released?
c. Is this an endothermic or exothermic reaction?
d. Is ΔH for this reaction positive or negative?
e. Would the ΔH be on the left or right side of the yield sign?
f. Is the reverse reaction exothermic or endothermic?
1) Enthalpy Changes in Problems
a. Convert to moles
b. Use conversion factor to find heat released or absorbed
Ex. How much heat will be released when 5.0g of H2O2 decompose.
2H2O2 → 2H2O + O2 ΔH = -190 kJ
Ex. How much heat will be released when 6.44 g of S reacts with an excess O2.
2S + 3O2 → 2SO3
ΔH = -791.4 kJ
10-2 & 10-3 Calorimetry
-The study of ____________ and ______________________.
-Calorimetry experiments – determine the heats of reactions by making
________________________ of temperature changes produces by a calorimeter.
1) Heat and Temperature
a. Heat Capacity –
b. Specific Heat
Formula for heat absorbed or released:
Remember: Specific Heat of Water = 4.184 J/g * ºC
Problem: How much heat is released when 501 g of water cools from 68.0 °C to
19.4 °C?
Problem: What is the specific heat of a nickel if the temperature of a 32.2 g
sample of nickel is increased by 3.5 º C when 50 J of heat is added.
Remember: q reaction = -q surroundings
Problem: When a 4.25 g sample of solid NH4NO3 dissolves in 60.0g of H2O in a
calorimeter, the temperature drops from 21.0 ºC to 16.9 ºC. Calculate H.
NH4NO3 → NH4+ + NO3-
2) Foods as Fuels
-Carbohydrates typically have ____________ enthalpies; however, the products of
their combustion, CO2 and H2O, have ____________ enthalpies.
-Therefore, the combustion of carbohydrates, especially fats, is ______________.
-Sugars and Starches break down to _____________, which reacts with O2 in a
combustion reaction.
- Nutritional information on food labels can be gathered using a calorimeter.
3) Hess’s Law
a) Hess states that if a series of reactions are _________________, the enthalpy
change for the __________________ will be the sum of the enthalpy changes of
the ___________________.
b) Steps for using Hess’s Law
1. Identify the Compounds
2. Locate the compounds on the periodic table.
3. Write a reaction from the table.
4. Write appropriate “sub equation”
i. If needed, multiply equation and enthalpy change.
ii. If you reverse the equation, change sign of enthalpy change.
5. Add equations.
6. Add enthalpy changes.
-Examples
Calculate ΔH for the following: C(s) + H2O(g) → CO(g) + H2(g)
Calculate ΔH for the following: 2CO(g) + O2(g) → 2CO2(g)