Chem/Phys Deck 3: Thermodynamics, Heat & Kinetics

What's the difference between heat and temperature?

Temperature: Average kinetic energy of particles.

Heat: Energy transferred due to a temperature difference.

Can two objects have the same temperature but different amounts of heat?

Yes! Heat depends on mass, specific heat, and temperature change

What is the equation for heat gained or lost?

q=mcΔT

m = mass

c = specific heat

ΔT = final − initial temperature

Which substance heats up faster: one with a high or low specific heat?

A low specific heat.

It takes less energy to change its temperature

Why does water warm up and cool down slowly?

Because water has a high specific heat capacity

During melting or boiling, does temperature change?

No.

The added energy breaks intermolecular forces instead of increasing kinetic energy.

During a phase change, where does the added energy go?

Into changing the phase (potential energy), not raising the temperature

Which phase changes are endothermic?

Melting

Vaporization

Sublimation

Which phase changes are exothermic?

Freezing

Condensation

Deposition

What does a positive ΔH mean?

Endothermic reaction.

Heat is absorbed.

What does a negative ΔH mean?

Exothermic reaction.

Heat is released.

What is the Gibbs free energy equation?

ΔG=ΔH−TΔS

If ΔG is negative, is the reaction spontaneous?

Yes

If ΔG is positive?

Not spontaneous

If ΔG = 0?

The system is at equilibrium

What is entropy?

A measure of disorder or the number of possible arrangements of particles

During melting, what happens to entropy?

Entropy increases

What is the rate law?

The relationship between reactant concentrations and reaction rate, determined experimentally

Does changing the coefficient in a balanced equation automatically change the rate law?

No.

Rate laws come from experiments, not stoichiometry.

What does a catalyst do?

Lowers activation energy and speeds up the reaction

Does a catalyst change ΔG or Keq?

No.

It only changes how quickly equilibrium is reached

What is activation energy?

The minimum energy needed for a reaction to occur

What happens to activation energy when a catalyst is added?

It decreases

At equilibrium, are the forward and reverse reaction rates equal?

Yes

Does a spontaneous reaction have to be fast?

Spontaneous means thermodynamically favorable, not kinetically fast.

Can an endothermic reaction be spontaneous?

Yes.

If the increase in entropy is large enough to make ΔG negative.

What's the difference between kinetics and thermodynamics?

Kinetics: How fast a reaction occurs.

Thermodynamics: Whether a reaction is favorable.