Thermochemistry Chapter 15 Part I –Physical Changes of Water.

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Presentation transcript:

Thermochemistry Chapter 15 Part I –Physical Changes of Water

Factors that influence heat change (q).

Heating curve: Ice  Water  Steam (H 2 1 atm) Energy Added Temperature

Critical Information 4.18 J = 1 cal  q = mc  T (same phase energy change)  q = m  h (phase change) c ice = 2.1 J/g o C c water = 4.18 J/g o C = 1.00 cal/g o C c steam = 1.7 J/g o C  h fus = 334 J/g  h vap = 2261 J/g

Heating Curve Problems You should be able to solve for: q total:

q total problem How much heat needs to be removed from 84 g of steam at 412 K to turn it into ice at 218 K?

Heating Curve Problems You should be able to solve for: Final temperature:

T f problem What is the final temperature if 78 kJ of heat are added to 22 g of ice at -14 o C?

Heating Curve Problems You should be able to solve for: % sample in two different phases:

% sample in two different phases problem How many grams of each phase will be present if 50 kJ of heat are added to 22 g of ice at -14 o C?

Heating Curve Problems You should be able to solve for: Mass:

Mass problem What is the mass of a sample of H 2 O if the addition of 35 kJ of heat takes it from 250 K to 415 K?

Heating Curve Problems You should be able to solve for: q total: Add the energy for each step on the graph Final temperature: Subtract the energy for each step from the total energy until the energy runs out during a step. Use the energy remaining for that step to solve for  T, T F. % sample in two different phases: Subtract the energy for each step from the total energy until the energy runs out during a plateau. Divide the energy remaining for that step by the total energy needed to change phase completely. Multiply the mass by this fraction. Mass –factor out m from each step.

Practice Problem A sample of ice at -25 o C is heated to steam at 200 o C by the addition of 300 kJ of energy. What is the mass of the sample?