Reactions and Energy

Define 'Enthalpy'

• a) Energy stored in the movement of molecules in a substance
• b) The opposite of temperature
• c) The temperature of a molecule
• d) Energy stored in the chemical bonds in a substance

ΔH value in an endothermic reaction is a positive number.

• True
• False

Which of the following examples is an endothermic reaction?

• Potassium Chloride dissolves in water the temperature drops.

• Acid mixed with Sodium Carbonate the temperature increases.

• Wood combusts and begins burning.

• A chemical reaction of phenol red and sodium bicarbonate feels hot to the touch

Which of the following describes an exothermic reaction?

• A drop in temperature

• Energy being absorbed

• Hot to the touch

• +change in enthalpy

In an endothermic reaction, energy is _________.

• absorbed

• released

____ reactions usually feel cold.

• endothermic

• exothermic

What type of reaction occurs in a hand warmer

• exothermic
• endothermic

If they energy required to break the bonds is greater than the energy given out by making new bonds the reaction is

• Exothermic
• Endothermic
• Neutralisation

If they energy required to break the bonds is less than the energy given out by making new bonds the reaction is

• Exothermic
• Endothermic
• Neutralisation

You perform a chemical reaction in class and find the change enthalpy  $\Delta H$  of a reaction is negative. What kind of reaction is it?

• Exothermic

• Endothermic