Praxis 5442 - Physical Science
Questions and Answers Latest Version
Graded A+
What is the primary reason gases expand to fill their container?
✔✔Gas particles move randomly and have negligible intermolecular forces
What happens to the pressure of a gas when its volume is halved at constant temperature?
✔✔The pressure doubles
What does the ideal gas law describe?
✔✔The relationship among pressure, volume, temperature, and number of moles of gas
What is the unit of the gas constant R when using pressure in atm and volume in liters?
✔✔0.0821 L·atm/mol·K
What type of process is described by a constant temperature change in a gas?
✔✔Isothermal process
1
,Why does increasing temperature increase the rate of a chemical reaction?
✔✔More particles have sufficient energy to overcome the activation energy barrier
What is the activation energy of a reaction?
✔✔The minimum energy required to start a chemical reaction
Why do chemical reactions generally occur faster in the gas phase than in the solid phase?
✔✔Particles move more freely and collide more often in the gas phase
What is enthalpy?
✔✔The total heat content of a system at constant pressure
What does a negative ΔH value indicate in a chemical reaction?
✔✔The reaction is exothermic
What is the main difference between an endothermic and an exothermic process?
✔✔Endothermic absorbs heat; exothermic releases heat
2
,What does Le Chatelier’s Principle predict about a system at equilibrium when pressure is
increased?
✔✔The system will shift to the side with fewer gas molecules
Why does adding a catalyst increase the rate of a reaction?
✔✔It lowers the activation energy required for the reaction
What property of a gas is directly proportional to its temperature in Kelvin?
✔✔Kinetic energy of the gas particles
What is the effect of decreasing the temperature on an endothermic reaction at equilibrium?
✔✔It shifts the equilibrium to the left (toward reactants)
Why does water have a higher boiling point than methane?
✔✔Water forms hydrogen bonds, which are stronger than the dispersion forces in methane
What is entropy?
3
, ✔✔A measure of the disorder or randomness in a system
What happens to entropy when a solid turns into a gas?
✔✔Entropy increases
Why does a balloon shrink when placed in a freezer?
✔✔Gas particles move slower, reducing internal pressure and volume
What is the relationship between intermolecular forces and boiling point?
✔✔Stronger intermolecular forces result in higher boiling points
What does the collision theory of reaction rates state?
✔✔Reactions occur when particles collide with proper orientation and sufficient energy
Why does increasing surface area increase the rate of a solid reacting with a liquid?
✔✔More surface is exposed, allowing more collisions between reactants
What is the standard state of a substance?
4
Questions and Answers Latest Version
Graded A+
What is the primary reason gases expand to fill their container?
✔✔Gas particles move randomly and have negligible intermolecular forces
What happens to the pressure of a gas when its volume is halved at constant temperature?
✔✔The pressure doubles
What does the ideal gas law describe?
✔✔The relationship among pressure, volume, temperature, and number of moles of gas
What is the unit of the gas constant R when using pressure in atm and volume in liters?
✔✔0.0821 L·atm/mol·K
What type of process is described by a constant temperature change in a gas?
✔✔Isothermal process
1
,Why does increasing temperature increase the rate of a chemical reaction?
✔✔More particles have sufficient energy to overcome the activation energy barrier
What is the activation energy of a reaction?
✔✔The minimum energy required to start a chemical reaction
Why do chemical reactions generally occur faster in the gas phase than in the solid phase?
✔✔Particles move more freely and collide more often in the gas phase
What is enthalpy?
✔✔The total heat content of a system at constant pressure
What does a negative ΔH value indicate in a chemical reaction?
✔✔The reaction is exothermic
What is the main difference between an endothermic and an exothermic process?
✔✔Endothermic absorbs heat; exothermic releases heat
2
,What does Le Chatelier’s Principle predict about a system at equilibrium when pressure is
increased?
✔✔The system will shift to the side with fewer gas molecules
Why does adding a catalyst increase the rate of a reaction?
✔✔It lowers the activation energy required for the reaction
What property of a gas is directly proportional to its temperature in Kelvin?
✔✔Kinetic energy of the gas particles
What is the effect of decreasing the temperature on an endothermic reaction at equilibrium?
✔✔It shifts the equilibrium to the left (toward reactants)
Why does water have a higher boiling point than methane?
✔✔Water forms hydrogen bonds, which are stronger than the dispersion forces in methane
What is entropy?
3
, ✔✔A measure of the disorder or randomness in a system
What happens to entropy when a solid turns into a gas?
✔✔Entropy increases
Why does a balloon shrink when placed in a freezer?
✔✔Gas particles move slower, reducing internal pressure and volume
What is the relationship between intermolecular forces and boiling point?
✔✔Stronger intermolecular forces result in higher boiling points
What does the collision theory of reaction rates state?
✔✔Reactions occur when particles collide with proper orientation and sufficient energy
Why does increasing surface area increase the rate of a solid reacting with a liquid?
✔✔More surface is exposed, allowing more collisions between reactants
What is the standard state of a substance?
4
