Chemistry 2 UNIT 6 Thermochemistry

What is energy?

The capacity to do work or produce heat.

What is work?

Anything that moves mass across a distance.

What are the two types of energy?

Kinetic energy and potential energy.

What is potential energy?

Energy due to position or composition.

What is kinetic energy?

Energy due to motion.

What is the law of conservation of energy?

Energy cannot be created or destroyed.

True or False: Energy can be changed from one form to another.

True.

What are particles of matter always doing?

They are in constant motion.

How is temperature related to kinetic energy?

Temperature measures the average kinetic energy of particles.

Which temperature corresponds to higher average kinetic energy?

Higher temperature.

Which temperature corresponds to lower average kinetic energy?

Lower temperature.

What happens to particle motion at absolute zero?

All kinetic motion stops.

What is absolute zero in Celsius?

-273°C.

What is absolute zero in Kelvin?

0 K.

Which temperature scale directly measures kinetic energy?

Kelvin.

What is thermochemistry?

The study of heat changes in chemical reactions.

What is heat?

The transfer of energy between objects at different temperatures.

What are the three methods of heat transfer?

Conduction, convection, and radiation.

What is another name for heat energy?

Thermal energy.

When does thermal equilibrium occur?

When two objects reach the same temperature.

What usually happens when heat is added to a substance?

Its temperature increases.

True or False: Heat always flows from warmer objects to cooler objects.

True.

What happens when two objects remain in contact?

Heat flows until thermal equilibrium is reached.

In thermochemistry, what is the system?

The part of the universe being studied.

What are the surroundings?

Everything outside the system.

True or False: Heat flows from surroundings to system in endothermic processes.

True.

What sign does heat have when a system loses energy?

Negative (−).

What sign does heat have when a system gains energy?

Positive (+).

What is the SI unit of energy?

Joule (J).

What is a calorie?

The amount of heat needed to raise 1 g of water by 1°C.

What is a kilocalorie?

1000 calories.

What is a food Calorie?

1 kilocalorie.

What variables determine heat absorbed or released?

Mass, temperature change, and chemical composition.

What is specific heat?

The energy required to raise 1 g of a substance by 1°C.

True or False: All substances have the same specific heat.

False.

What is the specific heat of water in J/g°C?

4.18 J/g°C.

What is the specific heat of water in cal/g°C?

1.00 cal/g°C.

What is enthalpy?

The total heat content of a system.

Can enthalpy changes be caused by physical changes?

Yes.

Can enthalpy changes be caused by chemical changes?

Yes.

True or False: Enthalpy changes only occur during chemical changes.

False.

What is calorimetry?

The accurate measurement of heat changes in physical or chemical processes.

Why is a calorimeter insulated?

To minimize heat transfer with the surroundings.

True or False: All calorimeters are sophisticated and expensive.

False.

In calorimetry, what causes the water temperature to increase?

Heat leaving the system.

True or False: For most systems, heat flow and enthalpy change are the same.

True.

What sign does ΔH have for an endothermic process?

Positive.

What sign does ΔH have for an exothermic process?

Negative.

In an endothermic process, does heat flow into or out of the system?

Into the system.

In an exothermic process, does heat flow into or out of the system?

Out of the system.

What equation is used for heat flow?

q = mCΔT

What does q represent?

Heat flow.

What does ΔH represent?

Enthalpy change.

What does m represent?

Mass.

What does C represent?

Specific heat capacity.

What does ΔT represent?

Change in temperature.

Can physical changes absorb energy?

Yes.

Can physical changes release energy?

Yes.

What is the energy required to melt a substance called?

Heat (enthalpy) of fusion.

What is the energy required to boil a substance called?

Heat (enthalpy) of vaporization.

What is ΔHfus for water?

334 J/g or 6.01 kJ/mol.

What is ΔHvap for water?

2257 J/g or 40.7 kJ/mol.

True or False: Both physical and chemical changes involve energy changes.

True.

Chemical reactions can either absorb or ______ energy.

Release.

Does breaking chemical bonds absorb or release energy?

Absorb energy.

Does forming chemical bonds absorb or release energy?

Release energy.

What determines whether a reaction absorbs or releases energy?

The difference between energy required to break bonds and energy released when bonds form.

What is an exothermic reaction?

A reaction that releases energy.

What is an endothermic reaction?

A reaction that absorbs energy.

What type of diagram shows energy changes during a reaction?

Potential energy diagram.

In an endothermic reaction, are products higher or lower in energy than reactants?

Higher.

In an exothermic reaction, are products higher or lower in energy than reactants?

Lower.

What do thermochemical equations show?

Energy changes caused by reactions.

What does ΔH mean?

Change in energy (enthalpy).

What units are commonly used for ΔH?

Joules (J) or kilojoules (kJ).

Can thermochemical equations be written in more than one way?

Yes.

Where can energy appear in an exothermic equation?

On the product side.

Where can energy appear in an endothermic equation?

On the reactant side.

What is a reversible reaction?

A reaction in which products can react to form reactants.

In a reversible reaction, are reactants and products formed simultaneously?

Yes.

What is chemical equilibrium?

A state where forward and reverse reaction rates are equal.

At equilibrium, are concentrations of reactants and products necessarily equal?

No.

True or False: Equilibrium systems are static.

False.

What is the equilibrium position?

The balance point between reactants and products.

Can equilibrium systems respond to changes?

Yes.

Which direction shifts equilibrium to produce more products?

Right.

What does Le Châtelier's Principle predict?

The direction an equilibrium will shift.

What factors can shift equilibrium?

Concentration, temperature, and pressure.

True or False: Equilibrium systems adjust to minimize changes.

True.

What happens if reactant concentration increases?

More products are formed.

What happens if product concentration decreases?

More products are formed.

How should energy be treated in equilibrium expressions?

As a reactant or product.

Cooling an equilibrium favors which type of reaction?

Exothermic.

How many classical states of matter are there?

Three.

What are the three classical states of matter?

Solid, liquid, and gas.

Which state has a fixed shape and fixed volume?

Solid.

Which state has a fixed volume but variable shape?

Liquid.

Which state has no fixed shape or volume?

Gas.

True or False: Ice remains at 0°C until all of it has melted.

True.

Is energy absorbed or released when intermolecular forces are broken?

Absorbed.