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AP Chem: Heat
Thermodynamics
15
Chemistry
12th Grade
11/03/2010

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Cards

Term
  1. Exothermic
  2. Endothermic
Definition
  1. A chemical reaction which evolves heat.
  2. A chemical reaction which absorbs heat.
Term

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

Definition

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

Term

Reverse Reaction

 

What is the reverse reaction of

C + O2 → CO2?

Definition

Products becoming reactants

 

C + O2 → CO2

(Forward reaction)

 

CO2 → C + O2

(Reverse reaction)

Term

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

Definition
ΔH forward is equal in magnitude but opposite in sign to ΔH reverse?
Term
  1. Hess's Law
  2. Molar heat of formation
Definition
  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.
Term

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

Definition

ΔH =

Σ(ΔHf—Products) — Σ(ΔHf—Reactants)

 

ΔH =

Heat of formation of reactants or products

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

 

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

Specific Heat

 

Give value for liquid water in calories and joules

Definition

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

 

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

 

Term

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

Definition

ΔH = mCT

 

 

Heat = (1 Cal./g- °C)

(10°C)(100g)

 

Heat = 1000 Cal.

Term

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

Definition

ΔH = mCT

 

ΔT = temperature change

Cp = specific heat

ΔH = heat absorbed or given off

Term
  1. Enthalpy
  2. Enthalpy Change  

      (State the equation)  

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

       ΔH = ΣHProducts-ΣHreactants

Term

Exothermic Reaction:

ΔH is ____1_____.

(positive or negative)

Enthalpy is ___2____.

(increased or decreased)

Definition
  1. Negative
  2. Decreased
Term

Endothermic Reacton:

ΔH is ____1____. 

(Positive or Negative)

Enthalpy is ____2_____.

(incraesed or decreased)

 

Definition
  1. Positive
  2. Negative

 

Term

List in the order of increasing enthalpy:

 

Solid, Gas, liquid

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

 

Term

Thermochemical

Equation 

Definition

A balanced chemical equatin which includes the enthalpy change.

 

H2(g)+1/2O2(g) → H2O(1) 

ΔH= -285kJ

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