Which segment best represents melting?

the energy required to change phase from solid to liquid

the energy required to change phase from liquid to gas

Temperature does NOT change during a phase change.

The graph best describes...

The graph best describes...

This energy curve is best described as an...

This energy curve is best described as an...

heat + reactants --> products

reactants --> products + heat

"The energy required to start a reaction."

"Speeds up a reaction by lowering activation energy."

Which best represents the activation energy of this exothermic energy curve?

Which number best represents the impact of a catalyst on the energy curve of an exothermic reaction?

Which color arrow represents the activation energy after a catalyst has been added to the reaction?

Enthalpy is defined as...

If the change in enthalpy is negative: $\Delta H\ =\ -$  

then the reaction is... 

If the change in enthalpy is positive: $\Delta H\ =\ +$  

then the reaction is...