1. Exothermic
2. Endothermic

1. A chemical reaction which evolves heat.
2. A chemical reaction which absorbs heat.

In a thermochemical equation, what happens to ΔH when the moles of reactants double?

Enthalpy is derctly proportional to mass. Therefore, when the moles double so does ΔH.

Reverse Reaction

What is the reverse reaction of

C + O₂ → CO₂?

Products becoming reactants

C + O₂ → CO₂

(Forward reaction)

CO₂ → C + O₂

(Reverse reaction)

How are ΔH for a forward and ΔH for a reverse reaction related?

1. Hess's Law
2. Molar heat of formation

1. ΔH for a reaction is the same regardless of the path travelled from reactants to products.
2. The molar heat of formation of a compound is equal to ΔH when 1mole of compound is formed from its elements at 1 atm. and 25º C.

Write the general equation to calculate ΔH for a chemical reaction.

ΔH =

Σ(ΔH_f—Products) — Σ(ΔH_{f—Reactants})

ΔH =

Heat of formation of reactants or products

1. what is the heat of formation of an element in its most stable state?
2. Calorimeter

1. Zero
2. A device of heat liberated or absorbed in a chemical reaction or physical change.

Specific Heat

Give value for liquid water in calories and joules

The amount of heat required to raise one gram of substance 1º C.

Water: 1 calorie/gram- ºC or 4.18 joules/gram- ºC

How many calories to raise 100 grams of water from 20° to 30° celsius?

ΔH = mC_pΔT

Heat = (1 Cal./g- °C)

(10°C)(100g)

Heat = 1000 Cal.

Write an equation to calculate energy change when a fixed mass of substance changes temperature.

ΔH = mC_pΔT

ΔT = temperature change

C_p = specific heat

ΔH = heat absorbed or given off

1. Enthalpy
2. Enthalpy Change  

      (State the equation)  

1. The heat content of a system.
2. The difference in heat content between the products and the reactants.

       ΔH = ΣH_Products-ΣH_reactants

Exothermic Reaction:

ΔH is ____1_____.

(positive or negative)

Enthalpy is ___2____.

(increased or decreased)

1. Negative
2. Decreased

Endothermic Reacton:

ΔH is ____1____. 

(Positive or Negative)

Enthalpy is ____2_____.

(incraesed or decreased)

1. Positive
2. Negative

List in the order of increasing enthalpy:

Solid, Gas, liquid

1. Solid (least enthalpy)
2. Liquid
3. Gas (most enthalpy)

Thermochemical

Equation 

A balanced chemical equatin which includes the enthalpy change.

H_2(g)+1/2O_2(g) → H₂O₍₁₎ 

ΔH= -285kJ