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Exambusters Chemistry Study Cards 10
Heat Cards (210-225)
23
Chemistry
10th Grade
09/01/2012

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Cards

Term
Exothermic
Definition
A chemical reaction which evolves heat
Term
Endothermic
Definition
A chemical reaction which absorbs heat
Term
Enthalpy
Definition
The heat content of a system
Term
Enthalpy Change (State the equation)
Definition

The difference in het content between the products and the reactants

 

ΔH = ΣHProducts - ΣHReactants

Term
Exothermic Reaction: ΔH is (positive or negative)
Definition
negative
Term
Exothermic Reaction: Enthalpy is (increasing or decreasing)
Definition
decreased
Term
Endothermic Reaction: ΔH is (positive or negative)
Definition
positive
Term
Endothermic Reaction: Enthalpy is (increased or decreased)
Definition
increased
Term
List in the order of increasing enthalpy: Liquid, Solid, Gas
Definition

Solid (least enthalpy)

Liquid

Gas (most enthalpy)

Term
Thermochemical equation
Definition

A balanced chemical equation which includes the enthalpy change.

H2(g) + ½O2(g) →H2O(l)

Δ H=-285kJ

Term
In a thermochemical equation, what happens to ΔH when the moles of reactants double?
Definition
Enthalpy is directly 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

CO2 → C + O2

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
Hess's Law
Definition
ΔH for a reaction is the same regardless of the path traveled from reactants to products
Term
Molar Heat of Formation
Definition
The molar heat of formation of a compound is equal to ΔH when 1 mole of compound is formed from its elements at 1 atm. and 25°C.
Term
Write the general equation to calculate ΔH for a chemical reaction.
Definition

ΔH = ∑(ΔHF(products)) - ∑(ΔHF(reactants))

 

ΔHF = Heat of Formation

Term
What is the heat of formation of an element in its most stable state?
Definition
zero
Term
Calorimeter
Definition
A device used to measure the quantity of heat liberated or absorbed in a chemical reaction or physical change
Term
Specific Heat
Definition
The amount of heat required to raise one gram of substance 1°C
Term
Give the specific heat value for liquid water in calories and Joules.
Definition
1 calorie/gram °C
Term
Give the specific heat value for liquid water in Joules.
Definition
4.18 Joules/gram °C
Term
Write an equation to calculate energy change when a fixed mass of substance changes temperature.
Definition

ΔH = mCpΔT

 

m = mass in grams

T = temperature change

Cp = specific heat

ΔH = heat absorbed, released

Term
How many calories to raise 100 grams of water from 20°C to 30°C
Definition

ΔH = mCpΔT

 

Heat = (100g)(1 cal/g°C)(10°C)

Heat = 1000 cal

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