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 0 elementos Total: MXN\$0.00 New videos from Khan Academy 2021-07-21T16:07:24.161336
Actualizado: hace 1 hora 29 mins

### Introduction to vector components

Vie, 2021-04-30 08:21
Vectors are quantities that have a magnitude and a direction. In the two-dimensional plane, we can describe them in an equivalent way, by thinking about the changes in x and y from the vector's tail to its head.

Vie, 2021-04-30 08:21
Vector quantities have both a magnitude and a direction. In this example, we interpret a mathematical statement about two vector quantities in terms of the real-world quantities they represent.

### Representing quantities with vectors

Vie, 2021-04-30 08:21
Vectors can represent real-world quantities where it's important to have both a magnitude and a direction. One example for that is force: you want to represent a force's magnitude (or strength), but it's also important to indicate in what direction the force is applied.

### Rule of 70 to approximate population doubling time

Jue, 2021-04-29 19:49
Practice using the rule of 70 to approximate population doubling time.

### Human population dynamics

Jue, 2021-04-29 19:49
Relate the trends amongst human population growth rate and human population size.

### Demographic transition model

Jue, 2021-04-29 19:49
Learn to apply the demographic transition model to populations.

### Tomb of Señora de Cao

Mié, 2021-04-21 19:37
The funerary bundle of the Señora de Cao, headdress ornament and six nose ornaments, found in what is now the El Brujo Archaeological Complex, c. 400 C.E., Moche (Museo Cao, Magdalena de Cao, Peru) A conversation with Dr. Sarahh Scher and Dr. Steven Zucker

### Tsimshian shaman’s rattle

Mié, 2021-04-21 19:17
Tsimshian, shaman's rattle, c. 1750–80, birch, bone, hair, pigment, and metal pins, made in British Columbia, Canada, 35.6 × 22.9 × 11.4 cm (The Metropolitan Museum of Art); speaker: Gaylord Torrence, Fred and Virginia Merrill Senior Curator of American Indian Art, The Nelson Atkins Museum of Art

### Constant-pressure calorimetry

Mar, 2021-04-20 04:25
Constant-pressure calorimetry is used to measure the change in enthalpy, ΔH, for a physical or chemical process. In this technique, a process is carried out in solution in a coffee cup calorimeter, an inexpensive device composed of two Styrofoam cups. The amount of heat transferred in the process (q) can be calculated from the mass, specific heat, and temperature change of the solution. Because the calorimeter is at constant (atmospheric) pressure, q is equal to ΔH for the process.

### Worked example: Using bond enthalpies to calculate enthalpy of reaction

Mar, 2021-04-20 04:25
Bond enthalpies can be used to estimate the change in enthalpy for a chemical reaction. In this video, we'll use average bond enthalpies to calculate the enthalpy change for the gas-phase combustion of ethanol.

### Enthalpy and phase changes

Mar, 2021-04-20 04:25
Energy is absorbed or released by a system undergoing a phase change. The energy changes for systems undergoing complementary phase changes are equal in magnitude but opposite in sign. For example, the molar heat of vaporization for water (corresponding to the transition from liquid water to gaseous water) is +40.7 kJ/mol, while the molar heat of condensation for water (corresponding to the transition from gaseous water to liquid water) is -40.7 kJ/mol.

### Heat transfer and thermal equilibrium

Mar, 2021-04-20 04:25
The particles in a warmer object have a greater average kinetic energy than the particles in a cooler object. When two objects of different temperatures come into contact with one another, the particles at the surface of each object collide, resulting in the transfer of energy as heat. This process continues until thermal equilibrium is reached, at which point the average kinetic energies of the particles—and therefore the temperatures of the objects—is the same.

### Constant-volume calorimetry

Mar, 2021-04-20 04:25
Constant-volume calorimetry is used to measure the change in internal energy, ΔE, for a combustion reaction. In this technique, a sample is burned under constant volume in a device called a bomb calorimeter. The amount of heat released in the reaction can be calculated using the equation q = -CΔT, where C is the heat capacity of the calorimeter and ΔT is the temperature change. Because the combustion occurs at constant volume, q is equal to ΔE for the reaction.

### Endothermic and exothermic processes

Mar, 2021-04-20 04:25
The first law of thermodynamics relates the change in the internal energy of a system (ΔE) to the heat transferred (q) and the work done (w). At constant pressure, q is equal to the change in enthalpy (ΔH) for a process. If ΔH is positive, the process absorbs heat from the surroundings and is said to be endothermic. If ΔH is negative, the process releases heat to the surroundings and is said to be exothermic. Phase changes, chemical reactions, and the formation of solutions are all examples of endothermic and exothermic processes.

### Enthalpy of formation

Mar, 2021-04-20 04:25
The standard enthalpy of formation of a compound is the enthalpy change that occurs when 1 mole of the compound is formed from its constituent elements in their standard states. A pure element in its standard state has a standard enthalpy of formation of zero. For any chemical reaction, the standard enthalpy change is the sum of the standard enthalpies of formation of the products minus the sum of the standard enthalpies of formation of the reactants.

### Worked example: Measuring enthalpy of reaction using coffee-cup calorimetry

Mar, 2021-04-20 04:25
Constant-pressure calorimetry is often used to determine the changes in enthalpy for aqueous reactions. In this video, we'll see how data from a coffee-cup calorimetry experiment can be used to calculate ΔH_rxn for the reaction between AgNO₃(aq) and NaCl(aq).

### Heating curve for water

Mar, 2021-04-20 04:25
The heating curve for water shows how the temperature of a given quantity of water changes as heat is added at a constant rate. During a phase change, the temperature of the water remains constant, resulting in a plateau on the graph. We can use the heating curve to calculate the amount of heat required to raise the temperature of the water sample by a certain amount, such as from -25°C (when the water is present as a solid) to 125°C (when the water is present as a gas).

### Heat capacity

Mar, 2021-04-20 04:25
Heat capacity is the amount of heat required to change the temperature of a given amount of matter by 1°C. The heat capacity of 1 gram of a substance is called its specific heat capacity (or specific heat), while the heat capacity of 1 mole of a substance is called its molar heat capacity. The amount of heat gained or lost by a sample (q) can be calculated using the equation q = mcΔT, where m is the mass of the sample, c is the specific heat, and ΔT is the temperature change.

### Enthalpy of reaction

Mar, 2021-04-20 04:25
The enthalpy change that accompanies a chemical reaction is referred to as the enthalpy of reaction and is abbreviated ΔH_rxn. The value of ΔH_rxn depends on how the balanced equation for the reaction is written and is typically given in units of kJ/mol-rxn.

### Worked example: Measuring the energy content of foods using soda-can calorimetry

Mar, 2021-04-20 04:25
Calorimetry is often used to evaluate the energy content of different foods. In this video, we'll see how data from a soda-can calorimetry experiment can be used to calculate the energy content of a marshmallow in Calories per gram.