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Describe an experience you’ve had making or building something where the amount of each ingredient or building block came in fixed ratios.

building a model airplane. For each model, there will be two wings and three wheels. In order for the model to look correct or work properly, there must be a certain, unvarying number of wings and wheels.

A chemical problem may be presented to you in units of moles, mass, or volume. Which one of these can be directly used in your arithmetic no matter what the conditions are?

Moles can be directly used. The number of molecules or moles is the basic unit used in solving chemical problems. When the number of moles are known, the mass and volume can be determined.

What is the importance of the coefficients in a balanced chemical reaction?

The coefficients in a balanced chemical equation indicate the relative number of moles of reactants and products. From this information, the amounts of reactants and products can be calculated. The number of moles may be converted to mass, volume, or number of representative particles.

What is the general procedure for solving a stoichiometric problem?

The coefficients from the balanced equation are used to write mole ratios. The mole ratios relate the moles of reactants to the moles of product. By multiplying the number of moles of the reactant by the mole ratio, you can determine the number of moles of the product.

In which kind of stoichiometric calculation can the steps involving conversion to and from moles be omitted? Explain why it is possible to do so.

Volume-volume conversions between gases do not require mole conversions. Molar volumes of all gases at STP are the same. The coefficients in a balanced equation indicate the relative number of moles and the relative volumes of interacting gases.

Assuming no errors were made in measuring the yield, can the percent yield of a chemical reaction be greater than 100%?

No: percent yield = actual yield/theoretical yield ´ 100%. The theoretical yield is the maximum amount of product that could be formed from given amounts of products. The actual yield must be less than or equal to the theoretical yield.


How does the pressure of an enclosed gas in a rigid container change when the gas is heated? Explain why this change occurs.

 The pressure increases when the gas is heated because increasing the temperature of the gas increases the average kinetic energy of the particles in the gas. With an increase in average kinetic energy, there will be an increase in the number of collisions between the particles and the container walls. In addition, because the particles are moving faster, on average, the collisions will occur with greater force. Both factors, the increased frequency of collision and the increased force of the collisions, contribute to the increase in pressure.

Explain how pumping air into a bicycle tire increases the pressure within the tire.

Adding air increases the number of gas particles in the tire. Collisions of particles with the inside walls of the tire cause the pressure that is exerted by the enclosed gas. Therefore, increasing the number of air particles increases the number of collisions, which in turn increases the pressure within the tire.

What are some of the differences between a real gas and an ideal gas?

An ideal gas is one that follows the gas laws at all conditions of pressure and temperature. The behavior of a real gas deviates from the behavior of an ideal gas, particularly at low temperatures and high pressures. Also, kinetic theory assumes that the particles of an ideal gas have no volume and are not attracted to each other. This is not true for real gases. Real gases can be liquefied and sometimes solidified by cooling and applying pressure, but ideal gases cannot.

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