Catching the heat of a reaction

Science · Chemistry · ages 16-17

Name ______________________ Date ____________

100 g of water rises 10 degrees. With c as 4.18, what is q in joules? Type the number.
Answer: ______________
A quoted enthalpy value means nothing without...
- Standard conditions it was measured under
- A bigger beaker
- A faster thermometer
A reaction that warms the mixture is exothermic and takes a negative sign.
Circle one: True False
4180 joules came from 0.05 mol. How many kilojoules per mole is that? Type the number.
Answer: ______________
Which mass goes into q equals mc delta T?
- The fuel burned
- The glass of the beaker
- The solution being heated
Why does the bench value fall short of the book value?
- The thermometer adds heat
- Heat leaks away and the reaction may not finish
- Water always boils
A student divides q by the moles of water heated. What is wrong?
- Water has no heat capacity
- You must divide by the moles of fuel, not water
- You should multiply instead
83.6 kilojoules per mole leaves the fuel. How is delta H written?
- Plus 83.6 kilojoules per mole
- Minus 83.6 kilojoules per mole
- With no sign at all

Answer key

For grown-ups. Fold this page away before handing over the rest.

4180 · Multiply 100 by 4.18 by 10.
Standard conditions it was measured under · Concentration, pressure and temperature anchor every value.
True · Warming means heat left the chemicals for the surroundings.
83.6 · Divide 4180 by 0.05, then convert joules to kilojoules.
The solution being heated · The thermometer watches the solution, so its mass counts.
Heat leaks away and the reaction may not finish · Lost heat and unfinished reactions both shrink the reading.
You must divide by the moles of fuel, not water · Per mole means per mole of reactant burned, the limiting one.
Minus 83.6 kilojoules per mole · Heat leaving means exothermic, which takes the negative sign.