A 25.0 mL sample of HBr is neutralized by reaction with 20.0 mL of 3.00 M KOH.  What is the concentration of HBr is the unknown sample? *hint- find the concentration of the base first.

The following reaction is an example of an ___ reaction. 2 N2(g) + O2(g) → 2 N2O (g)             ΔHrxn = +163.2 kJ

Consider the reaction below:        4Fe + 3O2 –> 2Fe2O3   If 44.2 grams of oxygen react with an excess of iron, what mass of Fe2O3 can form?  (Fe2O3= 159.70 g/mol)

A 1.0 gram sample of a candy bar was placed in a bomb calorimeter with a heat capacity of 3.54 kcal/°C. The sample was completely burned, causing the temperature of the calorimeter to rise by 1.36 °C.   How many kilocalories of energy were stored in the candy bar?    Make sure to show all your work- No work = no credit

Identify each of these reactions as endothermic or exothermic: a) heat + H2O(l)  –> H2O    b) H2O(g)  –> H2O(l) + heat c) K2CO3(s) –> K2CO3(aq) + heat d) heat+ NH4Cl(s) –> NH4Cl(aq)  

A chemist carries out this reaction in the laboratory, using grams of zinc and an excess of sulfur:  She isolated g of ZnS. Zn + S –> ZnS   Using the balanced equation, calculate the percent yield the chemist retrieved from the reaction.   What is her percent yield for this reaction?   percent yield= (actual yield)/(theo yield) *100%

The empirical formula for aluminum oxide is ___.  Make sure to leave no spaces.

In this reaction, the excess reagent is ___. 2Al + 5Br2  –> 2AlBr3   +  2Br2  

A chemist conducts a calorimetry experiment on an unknown metal. The mass of the metal is 24.4 g. The chemist heats the metal to 100 °C, then places it in a coffee-cup calorimeter containing 108.5 g of water.  The temperature of the water rises from 21.3 to 25.0 °C.   Useful equations: Cm= [mwCw(

When heated, zinc and sulfur combine to form a new compound, zinc sulfide, ZnS.  In this reaction,