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 heat—you can feel the surroundings get warmer as it proceeds.
Showing a random 20 of 50 problems.
Example 1
medium
Dissolving anhydrous CaCl2 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 ΔH=−90kJ and ΔS=−100J/K, use ΔG=ΔH−TΔS at T=298K to decide whether the (exothermic) reaction is spontaneous.
Example 5
medium
The combustion of octane releases 5470 kJ/mol. How much heat is released when 11.4 g of octane (M=114g/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 Ea and ΔH.
Example 7
medium
For a reaction, bonds broken absorb 840 kJ and bonds formed release 1020 kJ. Find ΔH and classify.Bonds broken: 840 kJ; bonds formed: 1020 kJ. Find ΔH and classify.
Example 8
medium
A 50.0mL acid-base neutralization in a coffee-cup calorimeter raises 100.0 g of solution from 21.0°C to 27.5°C (c=4.18J/g⋅∘C). Find q 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+O2→2H2O, ΔH=−572kJ per 2 mol H2. How much heat is released by burning 0.25 mol H2?
Example 11
medium
A reaction releases 890 kJ of heat per mole of methane burned. If 3.2 g of CH4 is burned (M=16g/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 ΔH? 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 ΔH=−200 kJ. Is it exothermic, and how much energy is released per the equation?A reaction has ΔH
Example 20
medium
On a reaction-energy diagram for an exothermic reaction, label the vertical distance from reactants down to products.Label the vertical distance from reactants down to products.