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### c0403

1. 1. Chemistry Item 04-03 Avogadro’s Law relates the volume and what variable?   A. moles B. pressure C. size of particles D. temperature www.upcatreview.com
2. 2. Chemistry Item 04-03 CONCEPT :   The properties of a gas may be described using the following variables: volume, temperature, pressure and amount in terms of no. of moles. Relating any of these variables with another comprise what is known as the gas laws. The following are the different gas laws: www.upcatreview.com
3. 3. Chemistry Item 04-03 <ul><li>The gas laws: </li></ul><ul><li>BOYLE’S LAW states that for any given mass of gas, the volume varies inversely with pressure at constant temperature. The law is also expressed as PV = k = constant and the general formula is </li></ul><ul><li>P 1 V 1 = P 2 V 2 </li></ul>www.upcatreview.com
4. 4. Chemistry Item 04-03 <ul><li>The gas laws: </li></ul><ul><li>CHARLES’ LAW states that for any given mass of gas, the volume varies directly with the absolute temperature, as pressure remains constant. It is expressed mathematically as V = kT and its general formula is </li></ul><ul><li>V 1 T 2 = V 2 T 1 </li></ul>www.upcatreview.com
5. 5. Chemistry Item 04-03 <ul><li>The gas laws: </li></ul><ul><li>GAY-LUSSAC’S LAW at constant volume, the pressure and absolute temperature of a gas vary directly. Mathematically, it is expressed as P = kT and its general formula is </li></ul><ul><li>P 1 T 2 = P 2 T 1 </li></ul>www.upcatreview.com
6. 6. Chemistry Item 04-03 <ul><li>The gas laws: </li></ul><ul><li>COMBINED GAS LAW For a given mass of gas the product of the pressure and volume divided by its absolute temperature is a constant. This can be expressed as PV / T = k </li></ul><ul><li>The general formula for this law is P 1 V 1 T 2 = P 2 V 2 T 1 </li></ul>www.upcatreview.com
7. 7. Chemistry Item 04-03 <ul><li>The gas laws: </li></ul><ul><li>AVOGADRO’S LAW states that equal volumes of all gases at the same temperature and pressure contain the same number of moles (molecules), n. This is expressed mathematically as </li></ul><ul><li>V = kn </li></ul>www.upcatreview.com
8. 8. Chemistry Item 04-03 <ul><li>The gas laws: </li></ul><ul><li>IDEAL GAS EQUATION describes the relationship between pressure (P), volume (V), number of moles (n) and absolute temperature (T K ) for an ideal gas. It is Boyle’s Law, Charles’ Law, and Avogadro’s Law combined into one mathematical statement: </li></ul>www.upcatreview.com
9. 9. Chemistry Item 04-03 <ul><li>The gas laws: </li></ul><ul><li>IDEAL GAS EQUATION </li></ul><ul><li>nT </li></ul><ul><li>V  ----- </li></ul><ul><li> P </li></ul>www.upcatreview.com
10. 10. Chemistry Item 04-03 <ul><li>The gas laws: </li></ul><ul><li>IDEAL GAS EQUATION </li></ul><ul><li>This statement can be written as a mathematical equation PV = nRT where R is a proportionality constant known as the ideal gas constant. It is equivalent to R = 0.0821 L-atm / mol-K </li></ul>www.upcatreview.com
11. 11. Chemistry Item 04-03 We use the concepts just mentioned to answer questions 1-3. Among the options in question #1, the formula which correctly describes Charles’ Law is V 1 T 2 = V 2 T 1 ( letter C ). Charles Law relates volume and temperature at constant pressure. www.upcatreview.com
12. 12. Chemistry Item 04-03 Question #2 is an application of Boyle’s Law since the problem relates the pressure with volume at constant temperature. According to Boyle’s Law, pressure is inversely related with volume that is as the pressure increases, the volume decreases and vice versa. www.upcatreview.com
13. 13. Chemistry Item 04-03 In the problem, the pressure is decreased to one-half the original pressure. In this case, the volume is expected to change opposite that of the change in pressure. Thus if the pressure decreased to one-half the original pressure, the volume will increase twice the original volume or will double ( letter A ). www.upcatreview.com
14. 14. Chemistry Item 04-03 Among the gas laws, Avogadro’s Law is the one which relates the volumes of different gases with the number of particles expressed in moles. Thus for question #3, the answer is moles ( letter A ). www.upcatreview.com