AP Chem: Heat – Flashcards

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

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

Products becoming reactants

C + O₂ → CO₂

(Forward reaction)

CO₂ → C + O₂

(Reverse reaction)

1. ;H 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 ;H when 1mole of compound is formed from its elements at 1 atm. and 25; C.

;H =

;(;H_f;Products) ; ;(;H_f;Reactants)

;

;H =

Heat of formation of reactants or products

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

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

;

Water: 1 calorie/gram- ;C or 4.18 joules/gram- ;C

;

;H = mC_p;T

;

;

Heat = (1 Cal./g- ;C)

(10;C)(100g)

;

Heat = 1000 Cal.

;H = mC_p;T

;

;T = temperature change

C_p = specific heat

;H = heat absorbed or given off

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

;;;;;;;;H = ;H_Products-;H_reactants

1. Negative
2. Decreased

1. Positive
2. Negative

;

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

;

A balanced chemical equatin which includes the enthalpy change.

;

H_2(g)+1/2O_2(g) ; H₂O_(1);

;H= -285kJ