Exo- and endothermic reactions

Which statement correctly describes energy and chemical bonds?

• Breaking chemical bonds releases energy.

• Forming chemical bonds requires energy input.

• Breaking chemical bonds requires energy input.

• Energy is neither absorbed nor released during bond changes.

In the reaction between acetic acid (C2H4O2) and sodium bicarbonate (NaHCO3), why is energy released when products form?

• Because atoms lose attraction and move apart.

• Because atoms with attraction are brought back together, forming bonds.

• Because no bonds are formed in the products.

• Because carbon dioxide absorbs all available energy.

Which description best defines an exothermic reaction?

• More energy is absorbed breaking bonds than released forming bonds.

• More energy is released forming bonds than is used to break bonds.

• There is no net energy change overall.

• Energy is used to form bonds but not to break them.

A reaction where more energy is absorbed when bonds in reactants are broken than is released when new bonds are formed in products is called:

• Exothermic

• Endothermic

• Isothermic

• Catalytic

Which scenario describes an isothermic reaction?

• The reaction releases more energy than it absorbs overall.

• The reaction absorbs more energy than it releases overall.

• The reaction absorbs as much energy as it releases, resulting in no net energy change.

• No bonds are broken or formed during the reaction.

Which comparison allows you to determine whether a reaction releases or absorbs energy overall?

• Compare the number of atoms in reactants and products.

• Compare the energy used to break bonds in reactants with the energy released when bonds form in products.

• Compare the masses of reactants and products.

• Compare the reaction rate and temperature.

Consider a reaction where bonds in reactants require 150 kJ to break, and bonds formed in products release 200 kJ. Which classification fits best?

• Endothermic, because energy absorbed is greater than energy released.

• Exothermic, because energy released is greater than energy absorbed.

• Isothermic, because energy absorbed equals energy released.

• Cannot be determined without the exact reactants.

Which observation indicates an exothermic reaction when monitoring temperature change in the reaction mixture?

• The temperature increases

• The temperature remains constant

• The temperature decreases

• The thermometer malfunctions

When energy is absorbed during a reaction, what typically happens to the temperature of the reaction mixture?

• It increases

• It decreases

• It stays the same

• It fluctuates randomly

Which statement correctly defines enthalpy change (ΔH) for a chemical reaction?

• ΔH compares the mass of reactants and products

• ΔH compares the energy of the reactants with the energy of the products

• ΔH measures the rate of reaction

• ΔH is the temperature of the reactants