1. Section 2: Heat
The enthalpy change for a reaction is the enthalpy of the products minus the enthalpy of the reactants. K
What I Know W
What I Want to Find Out L
What I Learned

2. 11(E) Use calorimetry to calculate the heat of a chemical process.
11(D) Perform calculations involving heat, mass, temperature change, and specific heat.
11(B) Understand the law of conservation of energy and the processes of heat transfer.
11(C) Use thermochemical equations to calculate energy changes that occur in chemical reactions and classify reactions as exothermic or endothermic.
11(E) Use calorimetry to calculate the heat of a chemical process.
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Heat

3. 2(F) Collect data and make measurements with accuracy and precision.
2(G) Express and manipulate chemical quantities using scientific conventions and mathematical procedures, including dimensional analysis, scientific notation, and significant figures.
2(I) Communicate valid conclusions supported by the data through methods such as lab reports, labeled drawings, graphs, journals, summaries, oral reports, and technology–based reports.
3(A) In all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student.
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Heat

4. Essential Questions
How is a calorimeter used to measure energy that is absorbed or released?
What do enthalpy and enthalpy change mean in terms of chemical reactions and processes?
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Heat

5. Vocabulary Review New pressure calorimeter thermochemistry system
surroundings
universe
enthalpy
enthalpy (heat) of reaction
Heat
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6. Calorimetry
A calorimeter is an insulated device used for measuring the amount of heat absorbed or released in a chemical reaction or physical process.
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Heat

7. USING SPECIFIC HEAT Problem Response KNOWN mass of metal, m = 4.68 g
Use with Example Problem 3.
Problem
A piece of metal with a mass of 4.68 g absorbs 256 J of heat when its temperature increases by 182°C. What is the specific heat of the metal? Could the metal be one of the alkaline earth metals listed in Table 2?
KNOWN
mass of metal, m = 4.68 g
quantity of heat absorbed, q = 256 J
ΔT = 182°C
UNKNOWN
specific heat, c = ? J/(g•°C)
Response
ANALYZE THE PROBLEM
You are given the mass of the metal, the amount of heat it absorbs, and the temperature change. You must calculate the specific heat. Use the equation for q, the quantity of heat, but solve for specific heat, c.
SOLVE FOR THE UNKNOWN
State the equation for the quantity of heat, q.
q = c × m × ΔT
Solve for c.
c = q m × ΔT
Heat
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8. USING SPECIFIC HEAT SOLVE FOR THE UNKNOWN (continued)
Substitute q = 256 J, m = 4.68 g, and ΔT = 182°C.
c = 256 J (4.68 g)(182°C) = J/(g•°C)
Table 2 indicates that the metal could be strontium.
EVALUATE THE ANSWER
The three quantities used in the calculation have three significant figures, and the answer is correctly stated with three digits. The calculations are correct and yield the expected unit.
Heat
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9. Chemical Energy and the Universe
Thermochemistry is the study of heat changes that accompany chemical reactions and phase changes.
The system is the specific part of the universe that contains the reaction or process you wish to study.
The surroundings are everything else other than the system in the universe.
The universe is defined as the system plus the surroundings.
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Heat

10. Chemical Energy and the Universe
Chemists are interested in changes in energy during reactions.
Enthalpy is the heat content of a system at constant pressure.
Enthalpy changes for exothermic reactions are always negative.
Enthalpy changes for endothermic reactions are always positive.
Enthalpy (heat) of reaction is the change in enthalpy during a reaction symbolized as ΔHrxn.
ΔHrxn = Hfinal – Hinitial
ΔHrxn = Hproducts – Hreactants
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Heat

11. Chemical Energy and the Universe
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Heat

12. Chemical Energy and the Universe
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Heat

13. Review Essential Questions Vocabulary
How is a calorimeter used to measure energy that is absorbed or released?
What do enthalpy and enthalpy change mean in terms of chemical reactions and processes?
Vocabulary
calorimeter
thermochemistry
system
surroundings
universe
enthalpy
enthalpy (heat) of reaction
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Heat