Which compound has 24 valence electrons? C3H6O C2H6O CO2 HCN

What is the correct electronic geometry and molecular geometry around the central nitrogen in NO2-?  (Hint:  you may need to draw the molecule.)  

A chemist carries out this reaction in the laboratory, using 4.31 grams of zinc and an excess of sulfur: Zn + S –> ZnS From the balanced equation, she calculates that she should obtain 6.41 grams of zinc sulfide.  However, she isolates only 5.85 g of product.  What is her percent yield for this reaction?  

 When a metal object is dropped into cold water, it releases 4,715 J of energy to its surroundings, and its temperature decreases from 100.0 °C to 20.0 °C.  The mass of the object is 420 grams.  What is the specific heat of this material?   0.210 J/g°C 4.59 x 106 J/g°C 4.76 J/g°C 85.0 J/g°C

Which of the following represents the freezing of water? H2O(s) –> H2O(l) + energy energy + H2O(s) –> H2O(l) H2O(l) –> H2O(s) + energy energy + H2O(l) –> H2O(s)

Which correctly describes a phase change concerning water?    I. Cooling water vapor can cause a phase change to liquid water. II. When liquid water gains enough heat it will change to a solid. III. When water vapor gets hot enough it will turn into liquid water.  IV. Cooling liquid water will cause a phase change to water vapor. 

An object with a mass of 5 kg is lifted vertically upwards by 10 meters. Calculate the gravitational potential energy of the object. (Acceleration due to gravity = 9.8 m/s²)

The blood transports more CO 2 in the form of ________ than in any other form. 

Each hemoglobin molecule can transport up to ________ oxygen molecules. 

What are the most numerous cells in the lungs?