Practice Exothermic Reaction in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

A chemical reaction that releases energy (usually as heat or light) to the surroundings, resulting in an increase in surrounding temperature and a negative enthalpy.

The reaction gives off heatβ€”you can feel the surroundings get warmer as it proceeds.

Showing a random 20 of 50 problems.

Example 1

medium
Dissolving anhydrous CaCl2_2 in water releases heat. Classify the dissolution and explain in terms of lattice energy versus hydration energy.

Example 2

easy
Does an exothermic reaction release or absorb heat?

Example 3

medium
A hand warmer relies on iron oxidation releasing heat. Classify the reaction and explain the heat felt.

Example 4

hard
For a reaction with Ξ”H=βˆ’90 kJ\Delta H = -90\,\text{kJ} and Ξ”S=βˆ’100 J/K\Delta S = -100\,\text{J/K}, use Ξ”G=Ξ”Hβˆ’TΞ”S\Delta G = \Delta H - T\Delta S at T=298 KT = 298\,\text{K} to decide whether the (exothermic) reaction is spontaneous.

Example 5

medium
The combustion of octane releases 54705470 kJ/mol. How much heat is released when 11.411.4 g of octane (M=114 g/molM = 114\,\text{g/mol}) burns?

Example 6

challenge
A reaction is exothermic but does not start at room temperature. A catalyst is added and it proceeds. Explain in terms of EaE_a and Ξ”H\Delta H.

Example 7

medium
For a reaction, bonds broken absorb 840840 kJ and bonds formed release 10201020 kJ. Find Ξ”H\Delta H and classify.

Example 8

medium
A 50.0 mL50.0\,\text{mL} acid-base neutralization in a coffee-cup calorimeter raises 100.0100.0 g of solution from 21.0 °C21.0\,Β°\text{C} to 27.5 °C27.5\,Β°\text{C} (c=4.18 J/g\cdotpΒ°Cc = 4.18\,\text{J/gΒ·Β°C}). Find qq released.

Example 9

easy
Fill in the blank: For an exothermic reaction, the enthalpy of the products is ____ than the enthalpy of the reactants.

Example 10

medium
For 2H2+O2β†’2H2O2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}, Ξ”H=βˆ’572 kJ\Delta H = -572\,\text{kJ} per 2 mol H2_2. How much heat is released by burning 0.250.25 mol H2_2?

Example 11

medium
A reaction releases 890890 kJ of heat per mole of methane burned. If 3.23.2 g of CH4\text{CH}_4 is burned (M=16 g/molM = 16\,\text{g/mol}), how much heat is released?

Example 12

easy
Acid-base neutralization warms the solution. What does this tell you about its energy change?

Example 13

medium
If a reaction is exothermic, what happens to the temperature of an insulated reaction mixture?

Example 14

hard
Two exothermic reactions release the same total energy: A is fast (seconds), B is slow (days). Does the difference in rate change Ξ”H\Delta H? Explain.

Example 15

easy
A reaction makes the beaker feel warm. Exothermic or endothermic?

Example 16

easy
Do exothermic reactions still need activation energy to start?

Example 17

easy
A hand warmer packet heats up when activated. Is this an exothermic or endothermic process? Explain.

Example 18

easy
A reaction mixture causes the beaker and surrounding air to become warmer. Is the reaction exothermic or endothermic? Explain.

Example 19

medium
A reaction has Ξ”H=βˆ’200\Delta H = -200 kJ. Is it exothermic, and how much energy is released per the equation?

Example 20

medium
On a reaction-energy diagram for an exothermic reaction, label the vertical distance from reactants down to products.
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