Heat & Enthalpy Changes in Chemical Reactions
Name________________________________
10.1 & 10.2 Review
Period________Date____________________
Matching: Write the letter of the definition that best matches the term.
________ 1. heat
A. reactions that release heat
________ 2. thermochemistry
B. the SI unit of energy and heat
________ 3. exothermic reactions
C. the energy that is transferred from one object to another
________ 4. endothermic reactions D. the study of the changes in heat in chemical reactions
________ 5. joule
E. example of an exothermic reaction
________ 6. combustion
F. reactions that absorb heat
True and False: Correct the false statements to make them true.
_____________________ 7. It is energy that maintains your body temperature close to 37 °C.
_____________________ 8. Bond breaking in chemical reactions releases energy.
_____________________ 9. Heat is transferred between two objects that are the same temperature.
_____________________ 10. An exothermic reaction absorbs heat from the environment.
_____________________ 11. All combustion reactions are exothermic.
_____________________ 12. If a reaction is endothermic, the amount of heat appears on the right side of
the arrow in the balanced equation.
_____________________ 13. Energy can be stored in the chemical bonds of a substance.
Problems: Solve each problem and then indicate whether it is an endothermic or exothermic reaction.
14. Calculate the amount of heat released by the combustion of 1.75 mol of benzene (C6H6).
2C6H6
+
15O2
→
12 CO2
+
6H2O
∆Hº = -98.0 kJ
15. How much heat is transferred when 100.0 g of calcium oxide reacts with carbon?
CaO +
3C
→
CaC2 +
CO
∆Hº = +464.8 kJ
16. Ammonium dichromate decomposes in a vigorous reaction when it is heated. Calculate the heat
transferred for the decomposition of 53.0 g of ammonium dichromate.
(NH4)2Cr2O7
→ N2
+ 4H2O
+
Cr2O3
∆Hº = -315 kJ
Completion: less
energy
endothermic
exothermic
change
pressure
standard enthalpy change
enthalpy
moles
1. The heat absorbed or released in a reaction depends on a quantity called ______________________.
2. The enthalpy of a substance is similar to, but not exactly the same as, the _____________________.
3. The symbol ∆H literally means a _________________ in enthalpy.
4. The ∆H for a(n) ______________________ reaction always has a positive sign.
5. In an exothermic reaction, Hproducts will always be _____________ than Hreactants.
6. Conditions such as temperature, _________________, and the physical states of the substances in a
reaction can affect ∆H.
7. The enthalpy change measured at 1 atm and 0 °C, when reactants and products are in their standard
states, is called the ________________________________________________.
8. You must know the number of _______________ of reactants involved in a reaction to calculate ∆H.
Short Answer: Answer the following questions in the space provided.
9. Provide an example from daily life that demonstrates how heat is transferred from one object to
another. __________________________________________________________________________
10. Provide an analogy that explains why bond breaking requires energy: __________________________
11. When ammonium chloride dissolves in a beaker of water, the beaker becomes cold to the touch.
Explain. __________________________________________________________________________
12. If you were given the ∆H° of a reaction, could you determine whether the reaction was exothermic or
endothermic? Explain. ______________________________________________________________
13. Compare the enthalpy of the reactants and the products in both exothermic and endothermic reactions.
__________________________________________________________________________________
14. What is meant by the standard state of an element (compound)? ______________________________